CYA over 100 with yellow/mustard algae

[MikeM]

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

[PoolDoc]

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!

[PoolDoc]

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

[MikeM]

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

[PoolDoc]

I'm glad to here you're going to try it; I'm really excited to see what happens.

Regarding mechanism -- phosphate is simply one of the key plant fertilizer components. If you garden (or farm), you've seen fertilizer ratings, like 10-10-10. These are NPK -- nitrogen/phosphate/potassium -- ratings and report the relative percentages of those plant nutrients in the fertilizer. You can use soil tests to find out if your soil needs more of one or the other nutrient, and match the fertilizer to the need, for example, applying 20-5-5 instead of 10-10-10.

Adding fertilizer, to match soil deficits, or crop needs, is what you do when you want plants to *grow*. Using phosphate remover is what you do when you do NOT want plants (algae!) to grow. Essentially, you are trying to remove, almost completely, a key plant nutrient: phosphates.

Please note that phosphate removal does NOT kill algae; it just makes it unhealthy and weak. You STILL have to chlorinate to kill it, but with low phosphates, it's much harder for the algae to recover from chlorine damage.

On many (most?) pools there's no need for this: chlorine destroys the algae just fine without weakening it by creating a phosphate deprived environment. But, some pools recurrently harbor chlorine resistant algae,

Why? I don't know!

But, on at least one such pool (the large country club pool I service), removing phosphates has resulted in substantial changes in the 'health' of the algae present. I don't yet know if this pool has previously had unusually high phosphate levels, or not. But I do know that with very low phosphate levels, the resistant algae this pool has ALWAYS harbored is not growing, and chlorine demand is way down.

I'm hoping that your pool, which has apparently also suffered recurrent mustard algae IN SPITE of high chlorine, may proved to be a second case. I'd *love* to be able to selectively recommend phosphate use, if it solves the problem some users have with recurrent algae.

[BigDave]

My pool also has had recurrent mustard algae problems despite high chlorine levels. I've kept it in check with slightly elevated FC and regular use of my robotic cleaner. Last year the robot failed and I went with brush and vacuum. The Yellow Beast started appearing in corners, liner seams and depressions in the floor. Several weeks of ++SHOCK++ levels and daily brushing didn't eradicate it.

My pool has solar panel heat and I use a solar blanket to retain heat. These may contribute to my difficulty removing the Mustard Algae.

I'd like to join this phosphate removal study this summer as well (now the pool is ice) - if I may.

Should I start a new thread or keep this all together here.

[PoolDoc]

By all means, please do. I'm particularly looking for people with some testing experience, so we can get a better idea of what's going on.

Let's keep the discussion altogether here, for now. If it's needed, I can pull apart the posts into two threads.