CYA over 100 with yellow/mustard algae

It's more definitive to do an overnight chlorine loss test by seeing the chlorine loss rate overnight by testing after the sun if off the pool in the evening and before it hits the pool in the morning. If your loss is less than 1 ppm FC, especially if 0.5 ppm or lower, then you don't have unusual loss. It doesn't prove you don't have algae, but it's not enough to show up as chlorine demand.

The main downside to a higher CYA level is that IF you get algae or any other reason for needing to shock the pool, it takes a LOT of chlorine to do so.

Chem_Geek is right about the very high chlorine levels required, if you do get mustard algae. But there are some ways to reduce that risk.

1. Using borax is probably the easiest and longest lasting, and has no undesirable side-effects. Like CYA, it's a permanent addition to the water. Unlike CYA, it is not subject to biodegradation. With a free form pool, your pool volume is only a guess, unless you actually measured it during filling, using the water meter. You'd need 20 - 25 boxes of borax + 5-7 gallons of muriatic acid, and some Lamotte borate strips (follow the link to the testkit page in my signature).

A borate level above 60 ppm reduces your pools susceptibility to algae quite a bit.

2. We don't normally recommend phosphate removal products, since if you keep your chlorine level adjusted, algae is usually not a problem regardless of phosphate levels. But, if you use them to lower your phosphates, and can avoid use of pool products containing phosphates, such as metal control products, then you can use phosphate removal products, during an algae episode, to lower levels so much that it virtually starves the algae. But, you'll need to test your fill water -- sometimes tap water has such high phosphates that this is not very practical.

3. Bromine. I'd consider this a sort of last resort. But adding sodium bromide to your pool, to produce a strong unstabilized halogen (bromine instead of chlorine) residual can also work. The downside is that your chlorine use will go WAY up during the period bromide is present, as it converts bromide to bromine. Eventually, things return to normal, since a small amount of the bromide is converted permanently to bromate on each conversion cycle, and the bromate is stable and doesn't interfere with pool chemistry.

If you choose to stay with high CYA, I'd recommend going ahead with borax. It doesn't cost that much, and gives you a margin of safety that's worthwhile. Waterbear, who has posted here for years, has found that it allows him to go on vacation for a week or so, without having to worry about algae on his return. He simply maintains chlorine levels, shocks before leaving, and then reports coming back to a clear pool. He reports that before borax, the pool was usually green on his return.

I agree that the borates are probably the best insurance -- they are a mild algaecide so might not prevent algae completely if the FC gets to zero, but they'll certainly slow down the growth enough to prevent things getting really bad and along with regular chlorine should help against tougher types of algae.

One other algaecide approach to Ben's list is an ammonium product such as ammonium chloride. With chlorine in the water, this creates monochloramine which kills algae (at least green algae; I'm not so sure about yellow/mustard algae, not enough experience with that). The main advantage with the monochloramine approach, unlike the sodium bromide, is that you can get rid of the monochloramine by adding more chlorine. With sodium bromide, it can take some time to get rid of the bromine, though by not overdosing it might not take more than some number of weeks and having a bromine pool is not a disaster (mostly it's just a higher chlorine demand for a while).

@ Chem_Geek

I've used monochloramine . . . and it works. But it's VERY irritating to swim in. In commercial pools, pre-season, 2 ppm got complaints from the guards and 5+ ppm ran them out of the pool with itchy red skin in minutes. Plus there seemed to be some sort of 're-bound' effect: the algae would clear, I'd achieve a CC< 0.5 ppm level, and then algae would return. It happened a couple of times, and I swore off the stuff, except for cleaning swamps.

I was focused on the outcome, and not on investigating what was happening, so I don't doubt that there may have been confounding factors. But it's left me very reluctant to recommend that approach.

I can testify it *does* result in a fast algae kill, and monochlor *will* penetrate sludge layers, rather than just oxidizing the top, like FC does.

It's fair to say, more research is needed. But I haven't had the opportunity.

Ahh... I was thinking about the pool not being used while the algae was being battled and not thinking about something being used on an ongoing basis. I completely agree with you that you can't use the monochloramine approach on an ongoing basis. Sorry about that. Brain fart.

Quote:

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Originally Posted by chem geek

Brain fart.

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Ah, yes. I wish I did not also suffer from those.

I find that one of the 'virtues' of having websites, like mine, with 1,000's of my words preserved by Wayback,etc. is that the stink can linger for years. :(

Hi Guys. I'm the OP on this thread, and thought I'd provide an update and ask a new question.

The yellow algae is back. It's in the same spot... where the floor and wall meet on a shady side, with a little less circulation than other areas. Last summer, with CYA in the 80-100 range, I raised FC to 20 and kept it there for about 3 weeks. I then let it fall and was maintaining between 8-12 all through Fall and Winter. There were probably 2-3 times I let the FC get below 8, but not for very long. The water looked very good until I noticed the algae was back about a week ago.

I want to whip this thing for good before swimming season starts. I checked CYA twice with the K2006 kit and also had the pool store check. Somehow it is DOWN to 32. It was very high 9 months ago (80-100). I have not drained any water and I have a cartridge filter, so I don't normally lose water. And of course, no slime over the winter. Question is: How could my CYA drop so much?

In any case, despite the surprisingly lower CYA, I have once again taken the FC up to 20 and I've maintained it there for the last week. I'm consuming 2.7ppm per day, which seems a little high. If any other suggestions on how to rid my pool of this beast, please let me know. Here are all my current numbers:

FC=22.5
CC=0
pH=7.6
TA=80
CYA=32
CH=250
Borates=50

Thanks for all the information and advice.

Mike

Perfect! (You're the droid I'm looking for . . .)

Mustard algae susceptible pools are one of the puzzles we have NOT solved here on the forum. It is definitely an issue that exists, but I've never figured out why. Having run as many as 25 large pools (>100,000 gallons) in a summer season, I saw problems with certain pools, year after year, but never saw those problems on other pools, even though the pools were operated with the same chemistry and with similar loads.

I tried every treatment I could -- quats, polyquats, copper, even Simazine when that was still legal. None of those worked. It's continued to be an issue from me, since the one remaining local pool I service (~200,000 gallons) has always been susceptible to mustard algae.

The only two treatments I had not tried were borates (> 50 ppm) and phosphate removers (PO4 < 200 ppb). I decided to try one or the other on my local pool this winter, and went with phosphate removers simply because it worked out to be cheaper. It turns out the fill water in that part of town may be the problem: phosphate levels, exiting the tap, are around 3 ppm or 3,000 ppb. I haven't checked with the water company, but that may be typical for water companies with lots of old iron pipe in their service area, since certain phosphates help reduce iron corrosion.

I started dosing in September, and got PO4 < 250 ppm by November. (I was concerned about filter problems, but didn't encounter any.) The results have been spectacular! My chlorine consumption is 20% of what it has been in previous winters, and yet there is no algae whatsoever.

Your results offer a data point suggesting that borates may NOT be a solution to this problem. If you're willing to try, your pool would make a great second test point, especially since you have had recurrent mustard algae. It you're willing to give it a go, you need to do the following:

1. Order the Taylor phosphate kit. I've tried 4 or 5 kits. Most are awful. The AquaChek is not as bad, but is really only readable at low levels -- you can use it once your phosphate is very low, but it's not going to help you find out how high it is now.

Taylor Technologies K-1106 Phosphate test kit
Hach Company 562227 Phosphate Test Kit (Aqua-Check)

2. Order 2 quarts of Clorox (was: Kem-Tek) phosphate remover (most phosphate removed per $ spent). If you like, you can wait to do this until after you've verified significant PO4 levels (ie, > 300 ppb).

Link to Chlorox brand phosphate remover DELETED -- product is HIGHLY diluted, and a very bad deal. Sorry!
Go to http://pool9.net/phosphates/ for current info

Kem-Tek is dropping its own brand, and replacing those products with identical ones bearing a "Clorox" label. Shipping from Amazon is currently delayed, because the product hasn't been distributed to all the Amazon warehouses, yet. There are also some reports of the Kem-Tek/Clorox product not removing what it should. For whatever reason this product seems to act more slowly than some others. Please wait a week before testing . . . but if you find that after a week it hasn't made the expected reductions, please post that info. Remember, only the Taylor phosphate kit can measure semi-accurately above 500 ppb (0.5 ppm).


3. Test your pool water, using a 3:1 dilution of distilled water to pool water. (Use distilled water in gallon jugs from Walmart). Multiply the result X4 for your PO4 level. If your PO4 level is low, you may need to test again, with no dilution. Assuming you find a significant PO4 level, THEN test your tap water, to get an idea of how much PO4 you're adding when you add water.

4. Once you're reading to begin lowering PO4, use *small* doses, and keep and eye on your filter. The pool I worked on has sand filters. DE filters may respond differently. The PO4 remover I used years ago clouded the pool and clogged filters, but I had no such problem this time. However, it may be different with DE, so start small and work up.

5. Meanwhile, maintain chlorine levels . . . and test water temperatures. Let me know what you find. I'm hoping you'll see the same results I did. I still don't think phosphate removers are for everyone, but I am really hoping they may be a solution for pools with recurrent mustard algae.

6. Ironically, solving the mustard algae problem *may* solve the disappearing CYA problem. Mustard algae forms a biofilm; some biofilms 'eat' CYA. It's possible the mustard algae biofilm is harboring bacteria that can eat your CYA.

Let me know; I'm excited!

My bad -- cartridge filter rather than DE. Still, that's a different type than sand, so go slow.

OK Ben, I'm game. I just ordered the Taylor phosphate kit. I'll hold off on the remover until I confirm my readings. I'll post my readings from the pool and tap after I get the Taylor kit.

Meanwhile, can you explain the cause-effect relationship between high PO4 and yellow algae? Or just refer me to some additional reading material?

Thanks,
Mike