Why is my pool so dirty!!!

[bizbad]

I have a 15000 gallon inground, completely screened in. It is about six months old. I check the water chemistry twice a week and everything has always been perfect and still is. But, starting about two months ago, if I dont brush my pool atleast three times a week I get brownish yellowish dirt buildup stuck to the sides and bottom and every nook and cranny. It brushes right off except for one spot now on my swimout that I actually think is stained from it. I think I may sell my house before the marcite is all stained.

[chem geek]

This sounds like you may have mustard algae as that is yellowish/brown and looks like dust or dirt. Can you post your water chemistry levels (FC, CC or TC, pH, CYA, TA, CH, Temp.)? It seems to take a higher level of disinfecting chlorine to prevent mustard algae (close to the Max. FC ranges in Ben's chart. It also takes a much higher level than the Shock levels to get rid of it. If you post your numbers, I can let you know what shock level will likely kill this stuff and what FC level you need to maintain to prevent it from returning.

[EDIT] What kind of filter do you have (cartridge, sand, DE, sand with some DE added) and how long do you run your pump each day? [END-EDIT]

Richard

[bizbad]

The "dirt" does look yellowish when I brush it you can see a yellowish almost orange cloud. I have a saltwater generator, FC 1.0 CC 0.0 PH 7.6 TA 100 CYA 70 temp right now is about 80 because I have the solar off so the ray vac cleans the bottom all day. pump runs 8 hours a day.

[Sully]

With your CYA of 70, your FC is way too low, at this level you should keep it maintained between 5-10ppm FC. Your going to have to boost your FC level up to at least 20 ppm to get rid of the mustard and keep it at 20. Along with daily brushings and keeping your filter running 24/7. Otherwise, the mustard is going to keep coming back. I fought with my pool for 2 months with mustard algae, before I got serious about getting rid of it for good.

[chem geek]

Sully is right, that your FC is way, way too low. You can try the 20 ppm FC to see if that kills the mustard/yellow algae, but users on this forum have found that this particular algae (which is chlorine resistent) takes a LOT more chlorine to kill. A couple of users needed to add enough chlorine (chlorinating liquid or bleach) to get to 1.0 ppm disinfecting chlorine (HOCl) concentration and with 70 ppm CYA that would take 47 ppm FC. Regardless of whether you target 20 or 47 ppm FC, you should lower your pH first to make the addition of chlorine more effective. You could first lower your pH to 7.2 (or even 7.0, but not lower) by adding Muriatic Acid. Then add lots and lots of chlorine. Let us know if the 20 ppm FC kills the mustard/yellow algae or not. I'm trying to keep track of the minimum level of chlorine needed to kill and prevent this form of algae.

After you've killed this algae, to prevent it from returning will likely require at least 5 ppm FC as Sully said, though in a non-SWG pool users have reported needing the equivalent of 11 ppm FC (for the 70 ppm CYA in your pool). Again, you'll have to experiment for your pool to see what level of FC will keep the mustard algae away, but it certainly will be far more than the 1 ppm FC that you had before.

Richard

[bizbad]

According to my pool company and my neighbors, and Aquarite the CYA and FC is right on the money. Why would the Saltwater generator company print incorrect water chemistry numbers?