Why does algae keep coming back on walls?

[shore1]

Since switching to BBB method last summer I am having a recurrent problem with algae just on the pool walls. It poofs up when brushed and is bright green. I will go through the shock process despite water being clear and cc 0 with no overnight fC loss. The chlorine did not go below 8-10 last 2 weeks (I have SWG by the way) and I kept it there and I still saw algae reappearing on walls. We brush once a week (I have a bad back). Filter pressure good at 10. From opening until a couple of weeks ago we even kept CYA at 55 and FC at 5 and we still got algae.

I am reluctant to go through mustard algae shock again on my vinyl liner as when I did that last summer along with pulling out pool light the algae still came back.

Note in my readings I have let the chlorine drop to 4 just because my husband doesn't like the chlorine so high (dries skin) and quite honestly it didn't keep the algae away. I did add polyquat after last shock.

I have a feeling our circulation is inadequate as we only have 2 returns plus pool vac return in a 30,000 gal pool. Should we just brush our pool more often and not worry about it as long as water is clear. I am just hoping to avoid that due to my back issues.


FC 4 (had been 8 at lowest)
CC 0
OFCL 0
PH 7.5
TA 75
CH 220
Borates 50
Salt 3200
CYA 75

 

[shore1]

I forgot to mention we have a large pond with algae in it about 40 yards from our pool. Could the spores go airborne? It's just odd the first two years the pool did not have this problem.

 

[woodyp]

Algae spores are definitely paratroopers!

 

[Richard320]

Not enough brushing would be my guess. I'll bet you don't get algae directly across from the return. Because it constantly blows fresh chlorinated water across that section.

Let's say the whole pool is perfectly and uniformly balanced. Now some dirt or spores blow into the pool. Where do they go? They stick to the walls. Don't ask me why - I just know stuff sticks to the walls from hard experience. Okay, so the chlorine goes to work on it. Now there's a chlorine deficiency right along the walls - maybe it's only 1/16", but it's there. Now if you brush, you scrub away the dead water and chlorinated water rushes in to fill the space.

 

[shore1]

My back was afraid you were going to tell me that! I'm open to any other suggestions if anyone has them though.