I wasn't sure if this should go in testing, pool opening, or algae forum - but since my numbers are weird, I thought I'd post here.
I think I'll go in chronological order, so the current stuff is at the bottom. Sorry this is going to be long I think, but want to give complete history.
BTW, I am using a TFT-100 test kit, bought about a year ago, stored inside the house. Pool is 17K gal. IG vinyl liner, Hayward sand filter. Northwest Florida (Pensacola).
Started to work on opening pool 2 weeks ago - green swamp. It hasn't been maintained over the winter due to having no work here so had to go out of town.
Mostly worked on getting leaves from the bottom, pH was high so added powder to reduce that. Put in liquid chlorine after a couple of days of general cleaning. I don't have those numbers anymore, and the process got interrupted.
8 days ago, tried again. I think most of the leaves and debris from the bottom are gone. Can't see, water green. The numbers I wrote down from my own test were TA 50, pH was above 7.8, CYA 31. No chlorine. Last year I had really good results from a bag of shock I got at Wal-Mart, and I so I tried using powdered first. I went to Leslie's and (yeah I know, probably stupid to listen to them) used 2 pounds of Coral Yellow Out - supposed to kill algae), waited half an hour, and used 1 pound of Leslie's Power Powder Plus (Cal hypo 73% available chlorine). 12 hours later, another pound and a half of Power Powder Plus. The entire time, running filter and scrubbing pool 1-2x daily. Saw ZERO effect.
Leslie's tested my water then, their results are FAC 0, CH 60, CYA 40, TA 90 pH 8+, Acid 5, Copper 0, Iron 0, TDS 800, Phosphates 200. They recommended a bunch more stuff, which I didn't buy.
I went back and got liquid chlorine 12% and started SLAMing per instructions. After 1 day, the pool had gone from dark swampy green to a light cloudy grayish green. Kept scrubbing, filter 24/7, kept chlorine around 16. After 2 days, not using much chlorine anymore. The water became just slightly clearer - I can now see the outline of the 3rd step in the shallow end - just barely, and when it first turned grayish green I could only see the 2nd step. About two days after it turned grayish I got a thin layer of white foam (tiny bubbles or just white "scum") on the surface.
I've continued with the SLAM, basically scrubbing daily, keeping chlorine back up to 16 when it gets low (I add 2-3x a day). It's never gone below 4-5. Filter on constantly. I added a little DE to the filter 4 days ago (in skimmer basket). The water looks the same for the past 5 days now. Cloudiness not really going. Backwash does show dirty water. Still getting very small amounts of leaves with rake every few days.
I did a full test today. Tested around 4pm, last time we added chlorine was about 22 hours ago.
CYA < 20 (this part seems weird - the tube was full and I could still see the dot, but after almost 24 hours and a sunny day, seems more chlorine would be gone if it was that low - and we've had a little rain, backwash, water going in with rake, but there is no way we've changed enough water to lower the CYA that much in a week?)
I guess the CYA could have been artificially high at first because the water was so cloudy/dirty with algae, but it's still impossible to see through in the pool (it looks clean in the sample - a week ago the sample was slightly greenish).
I also can't figure out why my pH has dropped THAT much - I added the stuff to lower it two weeks ago, and it didn't seem to lower it that much, but now it's going down down down.
Of course, what I want is clean water. I haven't done the overnight test since the water isn't clear, but I can if I need to. I'm not sure if I'm doing the right thing. Without being sure of the CYA, I'm not sure I should keep the chlorine levels so high (16). And I have no idea how to clear the cloudiness. It's going to be a few weeks probably before it's warm enough to swim, so I'm not in a desperate hurry, but I don't want to damage any of the equipment or waste money by keeping more chlorine in there than necessary, but I don't want to let it drop just in case, and end up with more algae.
Any suggestions greatly appreciated, and if this needs to be moved, please do (or I will repost if needed). If I've left out any info, please lmk. Thanks SO much!!!
(And btw, following the advice here and with my test kit last year, I successfully SLAMed the pool on opening, with liquid chlorine only, and it worked just fine - and I do remember it cleared faster, but it was warmer too. If any info has changed in the last year, I might have missed it though.)