Yellow/Brown dusty deposits that reappear repeatedly

I have a 24' ag pool that has been perfect until last week. I have been using the BBB method since installing the pool in July. However, late last week, we finally had some substantial rain (the first since May). Now, my pool has these brown deposits on the bottom. It tends to cluster in the little foot print divots and along the cove. It almost look like tannins from decayed leaves. But, I had just vacuumed the pool a couple of days before it started doing this.

I decided to brush it and the deposits easily stir up into a brown cloud that turns the pool a weak tea color. Overnight, the deposits settle down on the bottom again. I decided to shock the pool last night to see if it helps. I plan on vacuuming, but when I was brushing, the pole came apart and now I have to fish it off of the bottom and the water is cold right now. We had a low of 59* last night.

My tests results this morning:
FC: 8.5
CC: 0
CYA: approx. 25 (test doesn't show go lower than 30 but starts to cloud at 30)
TA: 60
Calcium: 130
pH: 7.2
1,500 ppm salt

Solar fish (in case this matters)

I added some more bleach after testing to get the chlorine levels higher and will retest in a couple of hours. I know that 8.5 isn't high enough yet. I want to get it to 12+.

Any ideas what this might be? I was thinking about adding DE to the sand filter and stirring up the brown again to see if it would help filter it out.

The filter is a 22" Hayward sand filter with a 2-speed Pentair 1.5 hp pump. I have been using low speed for the past couple of days.

SHOCK HARD - This stuff is the onset of some type of hard to kill Algae, it seems to start this time of year - probably something in the air and is very hard to kill off - I saw it last year this time, had a Heck of a time dealing with it until I overshocked, (15PPM does NOT even matter to it), I held it up at 20-25 for 24 hrs THEN it finally cleared. Got the onset of it this year - about a week ago, but remembered last year and overshocked right away, no problems at all getting it out. It's almost like a clay dust - dark brown - piles on floor just like you describe, shock, stir it up, use DE to filter it out since it's so fine it blows through - add flock 2 days after shocking, this really helps speed up the cleanup.
Definitely not mustard algae, but some other form - my neighbour got it about 4 days after us this year and the same time as us last year, did the same thing this year and it took care of it too.

That is exactly what you are describing. The one question that I have is why wouldn't I have combined chlorine if something organic is causing this. It is staying at 0, but the FC is being consumed at night. That is the one thing I tend to get confused about.

jstonemo,

You only get a CC>0 when the chlorine has incomplete oxidation of an organic or ammonia. That is, when chlorine first quickly combines with ammonia or a nitrogenous organic, it forms a chloramine which increases the CC, but with more chlorine this slowly breaks down to nitrogen gas and the CC returns to 0. Sunlight may also help further this breakdown process. Also, every time you add chlorine to your pool, you give it a very high concentration in a local area that also helps shock to breakpoint (this is also, presumably, how SWCG systems work, shocking locally in the salt cell). So in an outdoor pool with sufficient chlorine levels properly maintained, you usually see CC stay at 0. Generally, the CC becomes measurable if the chlorine is overwhelmed, say after a heavy bather load or rain with lots of junk blowing in the pool, but even this would likely be temporary if you continued to manually dose your pool with chlorine.

The fact that your chlorine is getting used up more than normal (especially overnight when the reduction in chlorine from sunlight doesn't occur) shows that the chlorine is indeed combining with something and it's most likely to be this brown spotted algae.

matt4x4,

I am curious as to what your CYA levels were when you needed to use 20-25 ppm of chlorine to zap this algae (and where 15 doesn't work). I'm trying to get a sense for the actual disinfecting chlorine level needed to kill various forms of algae, and this one sounds particularly hearty. Also, if you recall the pH when you killed the algae, that would also be helpful.

Thanks,
Richard

Hi Richard,
My CYA is steady at 20-30 ppm, probably started at around 30 in spring and slowly dropped over the course of the season to 20 as rain dilluted my water, I don't use much dichlor or trichlor, only a few pucks in the stairs to keep the chlorine concentration up inside them to avoid algae breakouts in there - very effective.
I didn't add any CYA this year because I opened to it being fine, and this late in the season I won't be bothered, rather keep the solar cover on during the day.
My alk and pH have also been in check all summer, it's been a relatively trouble free season, but every onset of fall I've seen this stuff creeping in, the funny thing about it is it is VERY slow to set in, you can keep your pool at 15PPM and it just slowly increases in mass, say over the course of a week, but you will not get it to go away, even if you don't do anything about it, it only creeps up on you slowly. The first time I saw it, I actually thought it was clay dust and attributed it to fields being tilled up the road, now I'm leaning more towards algae, especially since teh pool turns that tell tale blue once you do kill it off. I know ragweed is in bloom right now, I wonder if this stuff feeds off the pollen or something.
It's definitely not your typical common algae.
Oh, and tehy're not spots, rather like first described, it starts as a fine dust deposit in craters and at folds where the current would drop it, it eventually dusts teh whole floor if left alone, however, it does not "grab" on to the liner, even just creating a slight current above it will disperse it like dust and leave a spotless liner behind.

I just found this post - dealing with the same stuff - 20+ PPM cured it too.....although he's keeping the cl relatively high and still losing it daily - telling me the stuff's still lurking.....
http://www.poolforum.com/pf2/showthread.php?t=5471

And another - all in mid august onwards!

http://www.poolforum.com/pf2/showthread.php?t=5423

Thanks for the info. Well, if this stuff is algae, then it's pretty darn powerful stuff! At a pH of 7.5 and CYA of 30, the disinfecting chlorine (HOCl) level is 0.46 which is already pretty darn close to what I was thinking the "kill algae" level would be at 0.5. If it takes 20 ppm, then that is a disinfecting chlorine level of 0.88 (25 ppm is 1.6) so you can see that the disinfecting chlorine level rises up very rapidly with additions in FC because the FC is getting closer to the CYA level (overwhelming it).

If your CYA was 20 (instead of 30), then the 20 ppm FC gives 2.1 ppm disinfecting chlorine while 25 ppm FC gives 3.6 ppm disinfecting chlorine. So you can see how sensitive the numbers are in this range, making it hard to know what the true "kill level" is for this particular form of algae. If you throw in the inaccuracies of the various tests, especially for CYA, then it's really hard to figure this stuff out, but I appreciate the info nevertheless.

I suppose it's still possible that this stuff isn't algae and that the much higher chlorine levels are needed to oxidize it, though if it wasn't algae then I would figure it would just get caught into your filter or pool sweep. You mention the tell-tale blue that the pool turns after killing it off. I didn't know that is what happens with algae. I wonder if there is any other way to tell for certain if this stuff is really algae -- perhaps putting some into a beaker (covered with fine cloth to prevent other stuff from falling in) in partial sun and seeing if it grows would be one way to tell.

Richard

Richard, My guess is it's algae, it multiplies if left alone to the point where you get the heavy deposits in the craters getting even heavier, and an even film over the rest of the floor, I guess what i mean by "telltale blue" is the cloudy/white, but mixed with the background of the blue liner, it looks blue to me.
I will recheck my CYA tonite since i just dealt with this crap last week and it won't have changed from tehn, but I'm guessing it's somewhere closer to 20 than 30.

Even with DE in my filter, some (a lot) will get filtered out and looks green upon backwash, however, it comes back just as quick, and like i stated before 15PPM only slows it down, 20-25 has an effect. Dirt won't oxydize, so i know it's not clay dust - nor would my pool collect that much of it so quickly with a cover on it. And backwashing would be brown, not green.

Now, here's another observation my neighbour and i had the other evening - the air was just THICK with microscopic flying bugs, and I mean thick! No, it was not the beer we were drinking!
We couldn't see them if having the sky as the backdrop, however, get the trees as backdrop and you could see these things EVERYWHERE - now, maybe they're not the cause, but I could see that they may be the food keeping this stuff going.

Also, this year, I added salt to my pool, I thought salt was supposed to help deter algae as well, obviously not this stuff....

Hmm...

I walked out to check my pool this noon. I have this stuff in the corners of my deep end. Water looks great, is holding CL, but I still have this stuff.

I plan to vacuum it to waste tonight, then shock if it comes back. I'm not totally convinced it's algae. It could just be massive amounts of pollen/dust, but I don't know.

If I get a chance, I'll try to get a sample and run the test Richard mentioned.

after 3 years of dealing with this crap, and this year being the first where I was able to make it go away fast, I am convinced it's algae - unfortunately, I have none left in my pool to experiment with (well, maybe unfortunately is NOT the word I should be using...)
I have found several posts regarding the same stuff, all started mid august or later, this is a seasonal thing and because it takes chlorine (lots of it) to eliminate it, then it must be something organic. Since it multiplies, it's gotta be algae. I will be researching this further since it seems to be happening relatively frequently.

Ok, I found some algae with similar if not identical properties - called Brown Algae or Silica Algae - caused commonly through excess silicates and nitrates, inadequate light (like covering your pool because you're not using it much due to cooler weather).
Fed by things such as fertilizer - hmmm - fall, farmers fertilizing the fields before turning them over, me, living in the country? Anybody else in the country?

Anyways, that's all i have right now!

I live in a small town surrounded by country :)

Of course all our fertilizing was done in the spring, fields still have standing corn and beans. I don't cover my pool, but I don't know where silicates or nitrates would come from, have only used bleach. Having owned a pool for 12 years, this is the first year I noticed this stuff, and is also the first year I added salt. Coincidence? Perhaps the silicates are in the salt?

I don't live in the country, but close to it. I am in the KC suburbs on the edge of country land. My pool is not covered either. I have my FC over 20 right now and I am watching it. Gonna have to buy some floc and DE tonight.

Hi

I have been posting on another part of the forum. I have the same stuff. Mine started in July, really right after I put the pool up. I just thought it was dust/dirt from trees, and dirt/clay rd. I have been fighting this mess for awhile. Chlorine is above 25 for at least three days. Did dump 1/4 of water this morn and refilled. Been sweeping/vacumming. ETC. I do not have a way to backwash/ have a vinyl pool with the pump that came with it. I do have a new filter in it. Ok, it was like mentioned until I left to help dd with new baby. DH forgot to keep the chlorine up ..well when I came back it was dark green thru the whole pool. My pool today is a pretty blue with cloudy substance but notice the brown gunk when I sweep. Just like described. Ok, keep chlorine up but what happens when I let it drop back to swimming level, will that brown stuff come back? I havent got rid of it yet either. I do not cover it, I do live in the country, and my bro in law has his in full sun and he has it too. He does not cover his either. (lives next door) I havent been able to swim in the last two wks. I really would love to use the pool before cool weather sets in here in NW Fl panhandle. Thanks for any help. Oh, what is FLOC? And where do I get it? Thanks.

Floc is flocculant. It is a product that you add to the water that allows really fine particles to stick together into larger particles that your filter can catch and remove from the water. You can get it a your local pool store.

I was unable to get a sample of the stuff. It vaccuums up very easily, and doesn't act like any algae I've ever seen, but I do suspect it's some form of algae.

Wierd, my CL levels and use rates haven't changed, I'm still getting the same readings. My PH has crept up to over 8, so I need to knock it back down to increase my CL effectiveness. Perhaps that's why it was able to get started.

We've also had almost zero swimming activity in the pool for the past two weeks, which is never good for ultimate circulation.

Well, I had the CL levels at 23 ppm overnight last night and I added Alum to the filter to act as a filter aid. I woke up this morning and checked the pool. It is almost totally clear and clean. The CL level dropped to 19.5 ppm overnight, so something was being metabolized. In fact, after adding the bleach last night to get the levels above 20 ppm, I was in the yard and could smell the chlorine smell half way across the yard.

I don't think that adding 6.5 gallons of bleach to 12,700 gallons of water would make it smell so strongly. I am assuming it was chloramines from something breaking down. I can hardly smell anything this morning and the CL is still high at 19.5 ppm. I am going to try to keep it up near 20 for the rest of the day just to make sure everything is dead.

Had you vaccummed the pool before you shocked? If not did the "stuff" change color post shock?

I didn't vacuum. I did brush the bottom to get it stirred up into the water hoping that it would be better exposed to the chlorine. I am going to vacuum tonight or tomorrow.

I found some pics and descriptions of algae, and in turn, have to say that it may well be "Mustard algae" and not quite this brown algae i read about the other day. Mustard algae is one of those algaes that becomes resisitive to levels of chlorine up to 5ppm very quickly and may need levels as high as 30ppm to effectively kill it according to several articles i found - also, lots of brushing is required to fully expose it to the chlorine. Since this seems to be common when the swimming load dies off, your water is being mixed up much less, allowing this algae to take hold easier and quickly become resisitive to your typical sanitary chlorine levels.
I am still trying to find some sort of reference that may connect brown and mustard algae - from their descriptions, it may well be the same thing, just different terminology from different sources.....

Another couple of comments about mustard algae I found:

Yellow-green algae or xanthophytes are an important group of heterokont algae. Most live in freshwater, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filamentous forms. Unlike other heterokonts, their chloroplasts do not contain fucoxanthin, which accounts for their lighter colour. They appear to be the closest relatives of the brown algae.

YELLOW ALGAE: A wall clinging variety, also called mustard algae, is usually found on the shady side of the pool. It is sheet forming, and can be difficult to eradicate completely. Once begun, a pool owner could spend the entire season fighting yellow algae; reinfection is common. This variety is resistant to normal chlorine levels and must be dealt with firmly. Hit it hard!


Yellow Algae Phaeophyta: (Also called Mustard Algae), It creates a slimy layer that guards it from sanitizers. When brushed, yellow algae is removed easily but returns quickly. Yellow Algae can set in on any pool or spa. Chlorine may slow its growth, but will not completely kill this strain of Algae. An algaecide must be used to effectively kill and prevent this Algae.


Yellow algae is sometimes called mustard algae and appears on the pool surfaces as a fine dust. Typically it is seen first on surfaces that don't receive direct sunlight. This algae is easy to brush off, but it frequently returns. Most pool experts agree that this type is the most difficult algae to control. Use Sustain Algae Destroyer according to label directions and thoroughly brush the pool surfaces. Cleaning the filter and other equipment is especially important in controlling Yellow Algae. Circulate continuously and back-wash the filter/clean the element as needed to maintain good circulation. When the problem is under control, backwash the filter/clean the element regardless of the back-pressure/flow rate. This will rid the pool and equipment of any algae that may remain trapped in the filter.


Yellow Algae - This grown on the walls and when using your nylon brush it will dust up into a cloud. This is distinguishing between the two types.

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Brush your pool surface with nylon brush.
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Add a pound of granular shock per 10,000 gal. At the same time put in several capfuls of yellow treat. (There are several brands on the market, yellow out, yellow treat etc.)
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Circulate for half an hour then shut pool filter off for 23 hours.
Brush again before turning filter back on.
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After filter has run for 24 hours CLEAN YOUR FILTER. (If you don't clean your filter, then the algae will re-infect your pool water and you will have to start all over again!).
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Use a good non-metal based algaecide and this will help prevent yellow algae.
*
After using any kind of yellow out, yellow treat etc., be sure and do new test reading of your chemicals and readjust as needed



NOTE!!! - Above statements NOT entirely true - high concentrations of Chlorine WILL kill it off without the need of other chems - algaecide may help stop it from returning.





attached is a pic of what I found, if those steps are white and this stuff has set in good - like my pool year one, then this is definitely it.
Here's another link to a small pic and description that matches our issues.
http://www.poolgear.com/algae.html (am NOT pushing anything they sell, just here for the pic!)


OK, OK, That's enough now!! I gotta do some work!

cya!

Quote:

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Originally Posted by jstonemo

Well, I had the CL levels at 23 ppm overnight last night and I added Alum to the filter to act as a filter aid. I woke up this morning and checked the pool. It is almost totally clear and clean. The CL level dropped to 19.5 ppm overnight, so something was being metabolized. In fact, after adding the bleach last night to get the levels above 20 ppm, I was in the yard and could smell the chlorine smell half way across the yard.

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Man, this stuff is incredibly hearty. You had earlier quoted a CYA level less than 30 since it was getting cloudy at 30 (you said maybe 25, but it could be even lower than that). An FC of 20 with a CYA of 20 is a disinfecting chlorine (HOCl) level of 2.1 while at a CYA of 30 it is 0.9 so this is well above Ben's shock levels in his table and is higher than my own guess at 0.5 being sufficient to kill algae. It would seem that the easier-to-kill green algae seems to get killed over about a week at disinfecting chlorine levels of around 0.2-0.3 (so 0.5 would be faster), but this brown stuff needs somewhere between 1-2 ppm of disinfecting chlorine to kill. Yikes! Those people with high CYA in their pools are going to have a heck of a time killing this stuff. At 70 ppm CYA, it might take 46-58 ppm FC to kill this stuff.

As for the chlorine smell, yes you probably were smelling chloramines as intermediate by-products since these are formed rapidly. Then they are more slowly broken down (releasing nitrogen gas) and the smell goes away. This just shows that this brown stuff contains either ammonia or nitrogenous organics.

Richard

I do not understand the chemistry of vinyl liner fading so do not know exactly what level of chlorine will start to fade a liner. It has been written elsewhere on this forum that low pH does more to damage and fade a liner than chlorine, but obviously very high levels of chlorine can bleach dye out of most anything (as several pieces of my clothing with spots on them will prove -- I never wear anything good outside anymore when I dose with chlorine, no matter how careful I am).

Now that said, your CYA level of 40 will tie up most of the chlorine and in theory this chlorine tied up (combined with) CYA should not affect your liner, but I can't be certain of that.

I also do not know definitively precisely what level of disinfecting chlorine is needed to kill this mustard/yellow algae. It has also been reported elsewhere on this forum that using a polyquat algicide will help kill this stuff though generally the philosophy of this forum is to use chlorine whenever possible and save the extra chemicals only when needed (and this may be one of those times).

Refer to this chart and notice that to get 1-2 ppm of disinfecting chlorine (at a pH of 7.5) that appears to be needed to kill this algae, you would need (at 40 ppm CYA) somewhere around 25-35 ppm FC. Keep in mind that this will only give you the equivalent of 2-4 ppm FC if you were not using CYA, but again I do not know if this would damage or fade a liner (my guess is that it wouldn't if only exposed over a week or so -- a year, well maybe).

If you want to play it safe, you could try the polyquat algicide to see if that helps, especially if you are concerned with your vinyl fading. I personally don't think you'll run into a problem with the 25-35 FC level, but then again I don't have a vinyl pool nor your situation. If you do decide to go the "chlorine-only" route, start out at 25 and slowly work your pool up to 35 only if needed and please let us know what happens.

Sorry I'm not more definite about this.

Richard

P.S.
Your web-site is really nice!

Since I had to up my chlorine every august to 30-35 ppm when this stuff set in, I can tell you from experience that for the week or so that you need to keep the high chlorine settings, your liner will not fade, you probably get more fade from one month worth of sun.

I'm having the same problem with my ag pool. It started about 2 weeks ago. I got in to vacuum as cold as the water is this time of year and after I ran the filter for about 2 hours, I saw the same brown algae-like substance on the bottom but mostly in the middle area. My water is also a cloudy blue after vacuuming. I'm going to try doing a super shock but would like to know how much de to add to my sand filter. This stuff definitely seems to be blowing back in. When I backwash after vacuuming, there is only clear water coming through the hose. I'm also going to try using a filter saver (nylon skimmer sock purchased from In The Swim catalogue). Hopefully, if I vacuum with this sock in place, it will catch some of that dam BROWN STUFF. I've had an ag pool for the past 15 years with no problems but the past 2 years have been a nightmare. I didn't know that you could add de to a sand filter.

Back in mid July I posted the same issue and ultimately feel my filter is at fault and that this is not algae. We all seem to have Hayward sand filters, I don't know of any form of algae that just settles, it either is in suspension or attaches to something.
I know with my filter I can feel a slight suction on the return jet when I backwash and it took 7 days of 24 hour filtering to remove the cloud after spring shock so I'm pretty sure I have a bad spider gasket. Closing for spring I vacuumed to waste to remove the brown wonder and so far, 2 days later, nothing on the bottom. I will continue to check it over the next few weeks and report back.
Can someone siphon some out, put it in a glass and then shock the glass water and see the results? This should determine if it's organic or not.

Wayne

Wayne, this stuff we're talking about is DEFINITELY a type of Algae, it starts like deposits in spots, if left unattended, it gets to be more and more, what you don't really notice (until you start to vacuum) is that the whole floor will get a thin layer on it - it's so even that you think your remaining liner is spotless, however, turn the vac on and see the color difference. The walls also get it - more on the walls with shade and relatively hard to see.

That's it, when your pool water starts to look that aqua blue/green milky look, you're finally killing it off, another 3 days of filtering with the DE and you should be clean.
PIAlgae is what it SHOULD be called!

Quote:

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Originally Posted by RjBeals

I've had my cl levels at about 30 for 3 days now. pump on 24 hours/day.

Pool is definately clearing up.

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An FC of 30 with a CYA of 40 (that you mentioned in an earlier post) is a disinfecting chlorine (HOCl) level of around 1.3 ppm (an FC of 25 is an HOCl level of around 0.8 ppm) so it looks like we are narrowing down the amount of chlorine needed to kill this stuff to be a minimum of at least the column of 1 ppm in this table. If others have this problem with different levels of CYA (especially higher), then we can confirm this and eventually update Ben's Best Guess CYA chart to have at least two shock columns -- one for plain green algae (probably a 0.3 ppm level) and another for this mustard/yellow algae (probably a 1 ppm level). That leaves black algae where others have written about rubbing Tri-Chlor pucks on the algae, but I'm not sure about what overall pool chlorine levels are used at the same time to be effective.

Thank you all for keeping track of your chlorine (FC) and CYA levels during your battles with this algae. I know that the chemistry of what's going on is the last thing to enter your minds:eek:, but this information will ultimately help others.

Richard

OK, looks like were getting some good analysis going here. I'm not arguing that is not algae, I just think it's stil questionable. Maybe what I had/have is not the same thing. Does anyone know of a type of algae that just settles rather than attach? This is very interesting, maybe we are on to ta new strain???

Wayne

I have this same thing, started about 3 weeks ago. i thought at first it was from the dog getting into the pool. just put 3 big walmart ultra bottles in pool is about 12k gal. and have 3 more in the car. I vac the bottom sun and it was back tue. so i will keep the fc up about 20 for a few days and vac again sun and backwash.

Hello everyone!:)
I've been tring to find out what this stuff is myself!:confused: I had to drain and refill my pool about 2 weeks ago so the installers could add some more sand under my liner due to settling. I drained it down to about 2" then it rained the next day.
We got 3" of rain which sat in the pool for another day till the installers came to do the repair. Anyway, I started refilling the pool after they finished.
Once full I added 4lbs. of CYA, and 2GALS of pool store chlorine approx 6%.
I checked the CL. level the next day and it was 1.0 PPM so I added more to bring the level to 4 PPM which is where I wanted it. It held there for about 1 week then this stuff showed up.:( First I hand vacuumed and it came back a little at first then it got worse till it covered most of the bottom and I've been adding about 1/2 GAL of chlorine daily to keep the level at 3 PPM. Then I PANICKED.:eek: I went to the pool store ( Pinch-A-Penny) and let them sell me some Super Green Algicide.:o I dosed the pool with 4oz. as per directions.
and let it work for 24 hrs. then vacuum to waste buy hand. Looked real good just a little cloudy. This was yesterday, This morning I added 3/4 GAL of chlorine and went to work. I just got home and checked and I think it's back just a very little on the bottom so I have the auto-cleaner running now.
My numbers are CL 3.0
FREE CL 4.0
PH 7.4
CYA 40
COM CL 0.0
TO ALK 125
My pool is a 10,000 GAL Above Ground w/ a Clearwater 2600 sand filter What can I do? Help.

I think what you have put in your pool "super green" algaecide is an aglaecide that has copper in it. This being said, you may have a problem when you raise your chlorine to shock levels, as you may get some staining due to the copper in the algaecide which I read is 7%. Hopefully the algaecide has a sequesterer in it that keeps the copper in suspension. It really is not a good idea to introduce any metals in the water. High chlorine levels will kill any algae, you just have to keep it high enough long enough for it to do the job. With a cya of 40 you need to take your chlorine levels up to 15ppms and keep it there being very consistant. Everytime it falls below 15ppms, you have to add enough chlorine to take it back to 15. If you read through this thread, you will see this algae sometimes needs even higher levels of chlorine to kill it. I would suggest that you take your chlorine up to 15 - 20ppms and keep there, brushing and backwashing as needed. Be very consistant!!! You may want to drop your ph down to 7.2 while you are shocking the pool to help keep staining away. If you are consistant with the high chlorine levels, and keep your filter running 24/7, you should be able to get rid of this once and for all:D

I've been doing some thinking and looking at the numbers for this hard-to-kill yellow/mustard algae. Though it appeared that high chlorine levels were needed to kill this algae, my saying that it was around 1.0 ppm disinfecting chlorine (HOCl) assumed that the pH was around 7.5. Normally, the CYA acts as a chlorine buffer so higher pH doesn't change this concentration by that much, but this buffering starts to fall apart at the higher HOCl concentrations needed to kill this algae. What this means is that perhaps the actual disinfecting chlorine concentration needed to kill yellow/mustard algae is not 1.0 but is less, perhaps 0.7, but adding a lot of chlorine makes the pH rise which results in less disinfecting chlorine than I was assuming.

For practical purposes, using this chart when you start at around a pH of 7.5 and then add chlorine it is probably OK if you use the 0.3 ppm column (or at least 0.2) for green algae and the 1.0 column for yellow/mustard algae. However, next time this happens to someone, we should try to not only add chlorine to raise FC, but also start out at a lower pH (perhaps 7.2 or even 7.0) or add acid to keep the pH lower since that will allow for lower FC levels to kill the algae (meaning less bottles of chlorine and therefore lower cost).

I suppose this will have to wait until next August to see... Of course, everyone will probably be adding PolyQuat 60 and/or have 50 ppm borates in their pool and no one will get yellow/mustard algae so we can "experiment".:eek:

Richard

Can SOMEONE PLEASE STICKY this post, it contains very usedful information to a problem that seems to be reocurring frequently!
Also, if the title can be changed to "Yellow/Brown dusty deposits that reappear repeatedly" it may help.

Oh yeah, can it be cross stickied to the ALGAE forum too (because that just makes sense to me) ???? and maybe rated as 5/5 since it's helped many get rid of this crap through persistence even beyond the pool looking sparkling clean...

OK, Matt. I've done as requested. I am going to lock this particular thread, however, so we don't get people responding to both threads. If anyone wants to add any posts to this thread, please do so in the algae forum.

Thanks.