Pool is clear but bottom looks spotty and dirty

I had Algae issues last season and followed the advice this forum gives and it has been going well. I dont know if I started noticing more this season or that there is something going on with my pool.
First of all, I have to admit that I dont know what material my pool is made of. Usually I use a plastic brush to brush algae off the walls and the bottom, but since I saw lot of algae buildup last two months and they were so stubborn to remove with a normal plastic brush, I bought a wire brush and used a bit on the walls. I was a bit scared to use it liberally since they seem a bit harsh on the surface. But since I really dont know what the surface is made of I am not that confident about using them. I am attaching a picture with this and if someone could identify what type of surface my pool has, it will be really helpful.
There are lot of black dots/patches at the pool side and the bottom and I felt that after I brushed with the wire brush, I see black particles coming off the wall, I thought they were part of the pool surface (assuming the pool is some type of stone type material), it could be algae as well.
So, is it really okay to use the wirebrush on my pool? will it scratch or destroy the surface, is the black spots really because the surface is disintegrating? Or is it black algae?

Can you give us a complete set of numbers from the pool water especially CYA, FC, CC, pH and TA?

You'll really be lot happier if you invest in a K-2006 (or perhaps the k-2006C) because I think you might need to reach some pretty high shock levels to get this cleaned up but we won't know much until we have some reliable chemistry from the pool.

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Originally Posted by BigDave

Can you give us a complete set of numbers from the pool water especially CYA, FC, CC, pH and TA?

You'll really be lot happier if you invest in a K-2006 (or perhaps the k-2006C) because I think you might need to reach some pretty high shock levels to get this cleaned up but we won't know much until we have some reliable chemistry from the pool.

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Yes, I do have the Taylor kit. Here are the numbers, took just now.

FC - 3.2
CC - 0.4
CYA - Almost 30, but not quite.
pH - 7.6
TA - 125

I use the Clorox bleach from Costco and they recently upped the Sodium Hypo % to 8.25 and made the jugs smaller(121 fl oz). I seem to use lot of bleach but seems like I cant quite get rid of the Algae, and thought may be I am not scrubbing them off enough from the walls. Dont know if using the wire brush can damage the surface. The water is clear, but the surface appear to have lot of patches (seems they are algae).

Adding another closeup pic

I can't tell you if it's OK to use a wire brush - sorry.

It looks to me like the black stuff is something growing that will need to be killed. The fact that you've had algae recently, you have a measurable CC, and you feel you've been using excessive amounts of bleach supports the idea that you're fighting some bio-growth in the pool.

I'd recommend that you shock the pool. Are you familiar with the shock procedure recommended here? If not, a recap:

Raise the FC to shock levels (for your CYA level as per Ben's Best Guess Chart - use the 30-50 row as you're close to 30).
Test and restore FC to shock level as often as you can and don't let it fall below shock level.
Run filter 24/7.
Brush as often as you can (at least daily). The brushing is to expose the black stuff to the chlorine, not necessarily to scrub it all off.

Continue this process until one day after:

The pool is clear.
The pool loses less than 1 ppm FC between sunset and sunrise.
There's nearly no CC (less than 1 drop of R-0871 after adding the R-0003).

If there are no swimmers, maybe try the +shock+ level. I understand that black algae (if that's what this is) can hold strong to the tiny pores in concrete.

One other thought; If you use a 10 ml sample (multiply by 0.5 ppm instead of 0.2 ppm)for the FC and CC tests, your testing reagents will last longer.

Thanks BigDave.

FOr 8.25% bleach 121 fl oz jugs, can you tell me how many jugs I should pour each evening?

I am still concerned whether to use the wirebrush or not, they seem very effective, but if it is at the cost of damaging the surface i would be worried. On the other hand, the plastic brush seem not doing the job for me, Ive been using that.

Thanks again!

121oz. of 8.25% bleach should add about 5ppm FC to your 15K pool.

How much to dose depends on the measured FC level and how much you predict the pool will lose before the next FC measurement / dose.

Let's assume a 3ppm FC loss in a day and the last measurement is 3ppm FC. Three 121oz. jugs of 8.25% will add about 15ppm FC raising the FC to 18ppm. if the pool loses 3 ppm tomorrow, the remaining FC should be 15ppm - the minimum shock level. Then add a bit more than a half a jug to get back to 18ppm so the FC will be at least 15ppm the next time. NOTE - this is only an example - you'll have to put in your pool's loss rate

It's important to remember to measure - dose - measure and adjust as necessary. The more often you do this during the shock process, the better it will go.

As for the wire brush - you ultimately have to make that call. perhaps someone here will recognize your pool's surface and chime in but I have a vinyl and wouldn't go near it with a wire brush.

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Originally Posted by BigDave

121oz. of 8.25% bleach should add about 5ppm FC to your 15K pool.

How much to dose depends on the measured FC level and how much you predict the pool will lose before the next FC measurement / dose.

Let's assume a 3ppm FC loss in a day and the last measurement is 3ppm FC. Three 121oz. jugs of 8.25% will add about 15ppm FC raising the FC to 18ppm. if the pool loses 3 ppm tomorrow, the remaining FC should be 15ppm - the minimum shock level. Then add a bit more than a half a jug to get back to 18ppm so the FC will be at least 15ppm the next time. NOTE - this is only an example - you'll have to put in your pool's loss rate

It's important to remember to measure - dose - measure and adjust as necessary. The more often you do this during the shock process, the better it will go.

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Thanks! Yesterday, I did exactly what you said. I added 3 jugs and I analyzed the water after an hour. The data showed exactly what you said. Since I got it above 15ppm I thought that was good.

FC - 18.5 ppm
CC - 1.0

I analyzed the water again this morning and as you said, it got reduced to

FC - 13.5
CC - 0.5

Almost 5ppm loss. So I added a jug more awhile ago. And brushed the walls.

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As for the wire brush - you ultimately have to make that call. perhaps someone here will recognize your pool's surface and chime in but I have a vinyl and wouldn't go near it with a wire brush.

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I used the wirebrush anyway and seems like there is some improvement today (even though there is lot more to do). Probably I have a gunite surface. yeah, hope someone could confirm here

Another question, does adding bleach increase the pH, I think the pH increased to about 7.9. Or is it that the test is giving me false value at high FC level?

Also, should I add a bit more CYA ? And is CYA test values accurate at high FC level?

That is good but try not to let the FC go below 15ppm.

Shock levels will give falsely high pH readings - at 7.9, I wouldn't try to move it until the shock is over and FC returns to normal. I also wouldn't move CYA until the shock is over. Some people in warm, sunny areas like to run the CYA up to 90 to reduce total FC consumption and the frequency of adding chlorine - just remember to raise the minimum FC to correspond.

The black stuff may be easier to brush away after it's dead, just try to brush it enough to keep it exposed to the shock level water.

No new information, just to update that pool is looking a bit better, may be halfway through. Already backwashed the filter couple of times (pressure increased overnight to +6) and the skimmer (fine sieve) is catching lot of live algae(green). But loosing 5+ppm of Cl overnight. I guess it might be a better to add a bit more conditioner since I have below 30ppm CYA and the sun is brutal in Phoenix. And need to order more Taylor DPD-Titrant reagent as well before it gets finished. Thats all.
I am really interested to know how people remove algae without a wire brush. Big difference for me.

If you do decide to add more CYA, remember to raise the FC targets as well (for shock and regular maintenance).

I decided to wait before adding CYA since I am backwashing the filter almost every day. I put the CYA (granular) directly in skimmer and I am afraid it will all be gone when I backwash. Pool is still not looking completely clean. Its hard to remove them. And they dont seem to be turning brown at all, the algae that I catch are all the ones that I brush off from the walls and get caught in fine mesh skimmer and the filter. I was hoping that once I brush the walls a bit, algae should come off quickly and turn brown. I maintain the shock level of 15ppm all the time. The walls are a bit blackish, but the algae that get caught in the skimmer mesh is green.

I don't remember if you're using the pool yet or not. Perhaps you need to move to the +shock+ column of the chart. I recall reading that black algae can be very hard to kill and digs in to the pores in the surface and hangs on tight.

A couple other thoughts:
Is it still pollen season in your area? - might explain the green stuff in skimmer.
If the pollen is over and it's green(live) algae (wich clogs filters quickly), I'd guess that there's more CYA than measured or FC is dropping too low (Phoenix sun). Either way, my suggestion would be to raise the FC level to +shock+.

Yeah, I was just about to ask you if I should use a higher level for FC. No, they are algae (I think we have less pollen currently). Every time I brush they come out of the walls a bit by bit and get caught in the secondary skimmer after few hours(fine mesh) and the pressure of the filter rises +5 within next day or so. I backwashed the filter 4 times this week itself. The algae on the walls are not turning brown at all. They are still black and looks dark green when caught in skimmer mesh. To make matters worse I have a popup cleaning system (caretaker) which doesnt work well under high filter pressure. I have to maintain the sweet spot of 28-30psi or else they dont rotate, I think there is something I am unable to understand what to do.
I swim during the weekend, looks like good weather for this weekend, may be we will use it this weekend and start on the +shock+ levels. I will check CYA again tonight if its wrong. Thanks BigDave.

Wear an old swimsuit and have fun! :)
It's going to be a while for us - the pool made it up to 60 yesterday.

Here it is 101 today!

I have been continuously putting bleach and brushing the pool everyday for the past two weeks, maintaining atleast 15ppm of FC, I am starting to up the chlorine to 30 since I think its not that easy to get rid of them. The black spots are almost like plaster. Is there any thing else I can do to make it easier to shake them out and remove them? I am able to get rid of them, but only little by little and not sure if I can remove them completely. Its harder to remove them in the deeper part and under the water fall where it is hard to reach. Can I somehow brush them off with some concentrated chlorine or something?

I read in some other posts about using polyquat. Is that effective to remove black algae easily from the walls? Seems like I may be just losing the battle against the algae although I made huge progress, still algae is not completely removed even though I brushed the same place a 100 times, they are so stubborn. Unfortunately I was sick for few days and still recovering.. so physically I may not be able to do much brushing for couple of days as well.

Polyquat (the only algecide recommended here) is better at preventing algae than killing it. It also creates a chlorine demand when added to the pool. The best advice I can give is to maintain the +shock+ FC levels. Perhaps somone else will chime in with another idea.

I glad to hear you're making progress - don't give up.
I hope you feel better soon.

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Originally Posted by rkrgk

I am really interested to know how people remove algae without a wire brush.....

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My set up is totally different than yours but when I need to scrub the walls of my vinyl pool I use a stiff nylon brush. I thought maybe switching to a stiff nylon brush might be a good alternative for you if you think the wire brush is damaging the surface of your IG pool. Couldn't hurt trying it out.

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Originally Posted by robbym70

My set up is totally different than yours but when I need to scrub the walls of my vinyl pool I use a stiff nylon brush. I thought maybe switching to a stiff nylon brush might be a good alternative for you if you think the wire brush is damaging the surface of your IG pool. Couldn't hurt trying it out.

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I am having a tough time removing the black algae spots even with the wire brush. I think black algae may not stick to vinyl surface as it would to a gunite surface? I have scrubbed the walls everyday for three weeks continuously while maintaining a +shock+ level of FC, I got so tired, but still there are algae spots. I think there is has to be an easy way to remove them without draining and acid wash, but I just dont know what that is. Its almost gone, and is much better now, but I would like to remove the remaining patches somehow which does not come off even with a wirbrush. I was going to try some strong algecide as my next plan.

I'm sorry I can't give you a better plan, maybe some will read this who has another idea.
How's the pool surface holding up to the scrubbing? How are your numbers holding?
A couple warnings about algaecides:
Some have copper - not something most that really belongs in a pool - It can stain the pool, fingernails and blond and colored hair.
Some have ammonia which can combine with chlorine to form monochloramine ( an effective algaecide but stinky and irritating ) however a tremendous amount of chlorine will be consumed trying to overcome the ammonia and chloramines.
Some have Trade Secret - I'd never put that in my pool.

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Originally Posted by PoolDoc

Suggestions:

• Get a K2006 kit.
• Read the Best Guess Chlorine page.
• Adjust your chlorine levels to the correct range for algae killing -- use the low end of that range.
• Keep the chlorine there . . . for weeks.
• Begin brushing REGULARLY.
• Do not wear high-fashion expensive swimwear in the pool. Skin is VERY chlorine resistant; women's swimwear that costs over $100 is NOT. Such suits are made to be seen in, not to be swum in. If you use the pool a LOT, all polyester water aerobics suits are super-durable.

Black algae penetrates down into the cracks and crannies of the pool surface. Even when it seems to be gone, it's not. If you keep brushing while maintaining chlorine levels, it will be *mostly* gone 2 weeks after you can't see it any more.

But, it will not be all gone, and will recur if you let chlorine levels go low.

Note that if you have stabilizer levels above 40 ppm, and do not READ and FOLLOW the Best Guess Chart, you're mostly wasting your time. Keep in mind that test strips are HORRENDOUSLY inaccurate when use to measure stabilizer.

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I just saw that Ben had provided this advice to someone asking about Black algae. Perhaps we didn't need to go to +shock+ level but other than that we're consistent.
Please resist the urge to "throw stuff at it". Doing so will most likely make it much harder to clean.

Thanks BigDave for sending me the post from Ben.
My problem is that the remianing algae does not come off the pool surface at all. I was hoping there is an easier way to make chlorine reach these pores so that there will be progress when I scrub next time.

As I mentioned I did make lot of progress, whatever I could remove with my brush I removed them. And my numbers are not looking that bad (dont know why I dont use much Chlorine overnight with some black algae present still).
This is what I got yesterday evening and this morn.
FC - 8.5 (no change from last night)
pH - 7.8
TA - 150
CH - 400
CYA - 40ppm
Borate - 30ppm

As you can see I also added some Borax thinking it might help me control algae in the long term. I am ading some pics with this. Some of the spots that you see in the pic could be the shadow not the black spots. As you can see the walls and bottom are pretty clear of algae, but there still some.

Attachment 900Attachment 901

It makes sense that the overnight FC wouldn't change much with so little of the algae's surface area left exposed to chlorine.
I think Borate is a good choice - maybe a little higher. The pH might be getting a tad high (especially with 400 CH). Muriatic Acid is a good way to bring it back down - Be sure to read and understand:Using Muriatic Acid to Safely Lower Your Pool's pH.

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Originally Posted by BigDave

It makes sense that the overnight FC wouldn't change much with so little of the algae's surface area left exposed to chlorine.
I think Borate is a good choice - maybe a little higher.

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Yeah, I was following PoolDocs writeup on increasing to 50ppm, I got only 5 boxes of borax last time, I am planning to add 5 more, thats the reason my pH was a little off too.

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The pH might be getting a tad high (especially with 400 CH). Muriatic Acid is a good way to bring it back down - Be sure to read and understand:Using Muriatic Acid to Safely Lower Your Pool's pH.

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I did reduce the pH to 7.4 in the last two days.

I also got the polyquat 60 from amazon. And planning to add and see if it makes any difference. and may be get some trichlor powder and sprinkle directly on top of the black spots and brush if I can.

Sounds like a pretty goo idea - it will lower the pH locally so be on the lookout for pitting in the plaster.

One method I've read is to put the chemical in a zip-loc bag to transport it to the stain then pour / squeeze the slurry onto the target spots.

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Originally Posted by BigDave

Sounds like a pretty goo idea - it will lower the pH locally so be on the lookout for pitting in the plaster.

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Good point,yeah I somehow thought Trichlor is basic, when you mentioned I checked the Taylor booklet,its pH is 2.8-3.5. Hopefully wont stain, I guess I need to take a chance *rock and a hard place*.

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One method I've read is to put the chemical in a zip-loc bag to transport it to the stain then pour / squeeze the slurry onto the target spots.

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Sounds like a good idea. Let me go check if I can get some Trichlor powder locally here. I have the pucks from last year, but dont have a holder (like this, but got bad reviews.. http://www.amazon.com/Pentair-542068...pentair+holder) or else I could just use it to scratch the floor with it to get same effect I guess. shallow ends I could srub with the puck and see if it makes any difference. I will give it a try and let you know if it makes a difference.

Also do you know why it is bad to use ammonium hydroxide with chlorine in the pool? except that pool is unusable for few weeks. I read somewhere its effective against black algae.

You could break up a puck and put the chunks over the spots.

I wouldn't advise ammonia products in a pool - PoolDoc or ChemGeek may be able to advise you better - I just don't have the depth or chemistry. I do know that you'd be likely to form chloramines and that monochloramine is an effective algaecide - is does stink and irritate skin. If you want to use the pool, I'd stick with shock FC levels and wear old swimsuits.

The main reason ammonia products are used in a pool is that they form monochloramine that doesn't bind to CYA so in a pool with high CYA levels it's a way of "cheating" to get a higher active oxidizer level. This is especially true against algae that tend to look at monochloramine as if it were ammonia which is something they can use as a source of nitrogen, but the monochloramine kills them. However, your pool doesn't have very high CYA so shocking with chlorine should be quite effective. The key for black algae is to scrape off the waxy surface layer (the "heads") so that the chlorine can kill the algae below. Some people just maintain their pools at a somewhat higher FC level and brush regularly and the algae will slowly get killed while others go to shock level to try and get it over with more quickly -- up to you. At Ben's recommended FC/CYA levels, neither green nor black algae will be able to grow (yellow/mustard algae requires higher levels so is usually best to get rid of completely, if possible).

Thanks Chem Geek. I kept at shock level (15ppm+) for more than three weeks with daily brushing (yes daily, sometime twice a day) and for the last two weeks (of those three weeks) kept it at +shock+ (30ppm) level, still I could not get rid of all (or visibly none I should say) the black algae. Now I went back to keeping about 5-10ppm FC, since it got to a point where I had to say " I surrender" :). So I was looking at any other options I may have, to remove them before I resort to acid wash (if thats the only way). I feel that I have a higher chlorine demand because of the black alage on the walls, they seems to slowly grow as time pass (unless I keep shock level chlorine levels as per Bens chart which is not practical for more than a month or so). I think I wasted a lot of money trying to figure this out, but no real end in sight **tired** So I am a bit desperate to know what I am doing wrong with my approach. I am sure you guys, chem geek/PoolDoc have seen and encountered all kinds of these issues in and out, either I am not giving enough info or there is no possible recourse with my issue(black algae) using BBB or I don't quite understand it. Thanks BigDave too for trying to get to the bottom of my issue.

OK, so another option for you is to use Trichlor either as tabs or granular. The most common black algaecide is in fact Trichlor granular. The high chlorine level and low pH combine to be potent, BUT you can only use this on a plaster surface as it will destroy vinyl. Unfortunately, your concrete pool is painted so it would likely bleach out the paint, but if your paint is white then it might be OK. You could try a little in an area you don't care about and see if it leaves a mark. Of course, this method may work on the floor, but not for the walls.

Are you positive you have black algae? If you are able to scrape some off and spread it on a piece of paper, it should look dark green and not black. It is possible that you might have some metal staining instead. If you have metal stains, then lowering the pH of the pool would lighten them up. Also, putting some ascorbic acid (Vitamin C) would remove the stain if it were iron (if copper, then only the acid would lighten it).

It is black algae, I can scrape them and it is dark green, it looks tar-like when it is at the bottom and has tough texture and if I remove with a bit of force (from where I can) they float and are like algae. As I said in my previous post I was able to remove a lot of it using the wirebrush, and they were caught in the secondary skimmer (fine mesh) and they are green, granular and plant like. but it got to a point where it doesnt go away at all after 3-4 weeks.
I will use trichlor and let you know how that goes. I have trichlor tabs, but the problem is I dont know how to apply directly on top of them especially the walls. If I get the granules I can sprinke at the bottom to see if it makes a difference atleast at the bottom so I will know it works.

Your black algae must be very deeply rooted, but that seems very odd with a painted pool. Usually, scraping off the waxy layer and exposing the deeper algae to chlorine is enough to kill it. We look forward to seeing how the Trichlor granular works though as you point out I'm not sure what you'll be able to do with the walls in that case.

I think ours is a gunite construction, not painted concrete.

OK, then you need to change your signature because it says "18x32 kidney 15K gal IG painted concrete pool". That's why I made that comment.

I thought so too.. I changed the signature now. But I am sure I tried to change it a couple of times few months ago, but it was not saving my signature for some reason then, but I was able to this time.. weird