What is this residue and how do I get rid of it?

[swimmy]

I thought I might have mustard algae because there were brownish yellow spots on the bottom of the pool-always in the same places. I have treated with Yellow Rid and shocked numerous times and vacuumed to waste. The pool floor and sides remain clean until I turn the filtration system back on. Then the same places return in less than 12 hours. I'm sure its coming from the filtration system but how do i get rid of it? I have poured in sand cleaner at the recommended amount. The water is sparkling clear, but the residue on the bottom continues to return. It poofs and vacuums easily. What could it be????

[CarlD]

What are your numbers? I think your chlorine level is too low to kill it off.

[swimmy]

My test kit doesn't actually read higher than 5 but I keep it MUCH higher. I shocked using 6-8 bags of 62% calcium hypochlorite over 48 hours in addition to HTH algaecide initial dose, then continual pucks in the skimmer. I have a sand filter. The ph is 7.6. The water in the pool and the pool floor stay perfectly clear until I turn the filtration on. Is the stuff living in the system?

[Watermom]

You need to post a complete set of water testing results for us to really be able to advise you. (FC, CC, TC, PH, alk, calcium hardness and CYA) If your kit doesn't test for all these, give as many as you can, but we especially need to see a CYA reading. To make your test kit test higher cl levels, you can dilute your sample. Take one part pool water, and mix it with one part distilled water, test as usual and then multiply result by 2. If you need to go higher, one part pool water, two parts distilled, then multiply by 3, etc. With each dilution, you lose some accuracy, but it is better than nothing. You can buy a kit that tests higher than 5 at the sister site to this forum. www.poolsolutions.com

We also need to know the volume of your pool and if it is vinyl, fiberglass, gunite, etc. Welcome to the forum.

[swimmy]

Thank you so much! Will purchase a new test kit today. The pool is in-ground vinyl, 16x32, about 20,000 gallons. We've had it for 7 years and have NEVER had a problem. I don't think we've ever even used the vacuum hose until this year. The pool navigator has always done the trick before. The pool store folks say to change the filter sand every few years-but I know lots of people who never have. We haven't. Maybe that's the problem. Whatever it is turns white when I shock the pool but always returns through the jets.

[kbcpa]

I have an above ground pool and have been battling the same problem all season. I had something similar a few years ago and was told it was dead algae and to simply vacuum it to waste. We have done this over and over and when I turn the filtration back on in the morning the stuff reappears on the pool bottom within an hour. We have replaced the sand in the filter and thoroughly cleaned all the guts (laterals, etc.). What is this stuff and why won't it go away? Could the top part of my filter need to be replaced - the part where I can turn it to filter, waste, rinse, etc.?

Someone, please help!

My water is crystal clear.