Recurring Algae on Bottom of Pool

[chem geek]

Bob,

Since this is an above-ground pool, what is its configuration in terms of skimmers and returns? If it doesn't have a floor drain, then circulation near the deep bottom may be very poor and could lead to localized algae growth. Perhaps pointing one of the returns diagonally downwards can help with circulation.

I presume your 38 ppm CYA reading is an interpolated estimate since the test lines would show 30 or 40 ppm CYA.

The OTO test could be reading Total Chlorine (TC) so its possible that there is a lot of Combined Chlorine (CC) and not much Free Chlorine (FC), especially if there is algae. Also, be sure and take your pool water samples away from the return since the SWG will output higher FC there while you want to be measuring the bulk pool water. If there were some way for you to sample in the deep area near the algae, that would be good, but that doesn't sound easy to do.

[EDIT] I must say that it is extraordinarily rare to have a pool with such a fairly high FC/CYA ratio have this amount of algae. To even have the algae stirred up and stay green without turning cloudy from the chlorine is strange. Perhaps a FAS-DPD chlorine test will shed more light on this mystery. [END-EDIT]

Richard