Mustard Algae???

[chem geek]

I'm sorry your liner got bleached. Others who used the same high chlorine levels didn't get their liner bleached though they said that the sun will bleach it. Others with vinyl pools can tell you more about whether bleaching makes any difference. Typically, it's acidic conditions that are the problem with vinyl in terms of weakening it. Bleaching (which with chlorine is alkaline, not acidic) is just a color fading and doesn't represent any loss of integrity of the material itself. Did the liner just get bleached where you poured in the chlorine or is it bleached everywhere or just where the sun hits it, etc.?

Since your algae came back, you can try using PolyQuat algicide after you get rid of the algae (again -- using chlorine -- if your CYA is really 25, then you can use 20 ppm FC instead of 25 that you did before). I assume you cleaned out your filter after the algae was gone so as not to reintroduce it back into your pool. After killing the algae with chlorine, adding PolyQuat can help prevent it from coming back (you said it didn't work, but PolyQuat is better at prevention than killing an existing algae bloom and I'm not sure what you meant by "it didn't work"). Another option for you for preventative maintenance would be to use borates (50 ppm Boron from Borax), but that's a one-time decision to make. Evan and others now have Borate pools and are happy with it (see this thread for more info), but this is still preliminary and we don't know yet if such high borate pools would prevent this particular algae you are getting or not.

If you wanted to, you could experiment by taking two large buckets of your pool water that has this algae in it and try adding a very small amount of Borax to one of the buckets -- proportional to 50 ppm. It only takes 0.5 (that's one-half) of an ounce weight of Borax for 10 gallons to get 50 ppm. If the bucket with Borax (and maintained normal chlorine levels) kills and prevents the algae from growing while the bucket without Borax has the algae thrive, then you've got a plan. You can also use this technique to test out the PolyQuat as well (using another bucket or doing the experiment separately after washing out the bucket used for the Borates test) though you mentioned you had tried PolyQuat and it didn't work, but try killing the algae in the bucket with chlorine first and then see if PolyQuat prevents it from coming back.

Unfortunately, you didn't get the same positive results that others have seen in battling this algae -- you did get rid of it (visibly), but it came back. Carl and others may have some other suggestions that are of a "last resort" variety including testing for phosphates that is normally not done unless everything else does not work.

I also wonder if there is any remnant from previously being a Baquacil pool that could be causing an issue here. Perhaps others may know.

Richard