Hi, new pool owner here. I bought a place in April that has a pool, it's about 9500 gallons, pebble tech, Hayward 60 DE filter, vanishing-edge with a mostly clogged sheer-descent waterfall to return the water from the overflows to the main pool.
When I first moved-in, the water had been recently changed, but was very cloudy, filter pressure was at 36psi and would not go down with a backflush. I opened it up and the grids were totally collapsed, cracked, cloth bags torn. I replaced them and the pool cleared in about a day. The local poolstore told me that all I needed was some pucks (recommended 3-4 per week in 100degree AZ heat). You can guess what happened next, pool turned green, pool store then recommended Phosfree ($78), clarifier ($15), powdered shock ($5/#) etc. etc. etc.
I've gained and lost control of the pool several times over the last few months. The only time that things stay nice is when I added chlorine twice a day and specifically add it to the overflows for the negative edge every day (4oz bleach into each side). Even when the pool was not exploding with algae, it was taking a LOT of chlorine and if I didn't dose it twice a day it would rapidly drop to 0 and another outbreak would begin. I discovered TFP a while ago and have been reading and preparing. I got the TF-100 test kit and a ton of bleach and started a TFP shock last Saturday (FC:0, initial dose 3 gallons bleach).
My CYA was 58 due to the pool store guy telling me to just use pucks and the fact that the pool ate 40# of pucks 3-4months.
Chlorine consumption seems to have stabilized and I'm going to start letting it drift down. My overflows are relatively small, and in more direct sunlight than the rest of the pool. What I think is happening is that they consume chlorine MUCH faster than the pool itself, since they have more surface area relative to volume, are in direct sunlight & accumulate leaves they deplete their local supply of FC and get down to zero in the interval between when the pumps cycle and once the algae has a foothold there, consumption for the whole pool goes up and things spiral out of control. I have added additional trippers to the mechanical timers so that the pumps run twice a day instead of once (1-2pm & 6-11pm). The idea being that half-way thru the daytime, the water in the overflows mixes with the main pool water again to replenish its FC reserves. To test my theory, I checked the FC this morning at 9am, the main pool had drifted down to 20 from 24, but the overflows had drifted down to 19 (pumps stopped at 11pm). This seems to confirm my theory. TFP log attached. Any advice?