Recurring Algae on Bottom of Pool

I have a 16 X 32 AG with 6 ft deep center area and have an AutoPilot SWG.
Chemistry as follows (PS233):

CL > 5ppm (OTO only as DPD Reagent R0871 is on order)
PH 7.2
TA 80
CH 150
CYA 38
Salt 2270 (via AquaCheck test strip. Yes - a little low)

Filter = Sand

I typically run the chlorine a little high, but, whenever I leave the pool covered for several days(5-7), the bottom begins to turn green. First a light coat of algae forms and then if left for a couple more days the bottom begins to form heavier “streaks” of darker green. All this while the water stays very clear. Of course, once the kids enter the water and stir things up, the entire pool turns green and requires re-shocking, extensive filtering, and so on. I purchased the SWG in hopes to avoiding blooms like this. What am I missing?

Help! Bob

The numbers don't look bad, so...maybe the OTO isn't giving the readings you need.

If it is algae, you need to go on to a full-blown war to kill the algae, running your FC up to 15 and keeping it there for days, brushing an vacuuming daily.

Otherwise, something else is going on.....

War has begun. A couple more questions. With regard to daily brushing. If all algae have been killed, the water is clear, and the bottom and sides "look" clean/blue, but I haven’t brushed the pool adequately… Does this make it easier for algae to re-enter the pool? If the pool has been completely freed from algae (shock level CL for days and proper brushing till the water is clear), how often should I brush the pool?

I've got 4 kids, too many sports events, and I'm a little lazy to boot - so I'm looking for the bare minimum required to keep the pool clear of the green haze.

Thanks for reviewing my chem levels. As for the OTO reading – I just bought a new bottle of OTO so that should be ok.

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

Is it possible for algae to actually get into the liner? My liner is in need of replacing and has areas that are stained. This year algae has been the worst I have seen in years. I have brushed kept high levels of chlorine and it just keeps coming back. The liner is faded where you can hardly see any of the design other than on the walls and as I said there are light brown areas on the bottom. The water has just begun to get better (20 ppm chlorine for two days), but even now it seems to be returning. I see it on the steps. I will keep brushing and keep the chlorine level up, but was just wondering if it was possible for the algae to permeate the liner and thus be harder to kill.

the cya is about 30, ta 100, ph 7.6. I also added 40 ppm of Borax hoping it will help future attacks. This addition went without any problems as to ph fluctuations. The percentages on the other threads were exact.

Jay in NC

You might try putting all the "stuff" you use in the pool (floats, noodles, brushes, nets, etc) into the pool while it's shocked so that if there is algae growing on any of that stuff it will be killed and not re-introduced into the pool. Also check lighting sockets, ridges around pool steps, etc and make sure there's nothing hiding from you.

Janet

Well I finally got rid of the algae. 20 ppm bleach for 4 - 5 days won out. The liner still has light brown stains. Don't know what it is. I am going to keep it above 5 ppm from now on and hopefully it won't return.

Brown could be iron oxide or dead algae.