Pool opening - unsure if Black Algae-HELP

[gfritz1]

Intalled pump and got water circulating a week ago but left winter Loop Lok cover on . Check water and FC was at 9.0 and water looked clear .Have been running roughly a week as in Pa still very cold .Today took off the winter cover and water was clear .Vacuum and got everything up but noticed that we had a lot of stain or something on vinyl liner. We have been on bleach for three years and pool is a 23000 gal inground with a DE filter . We tried brushing and it did not work so I got out a pad (Scotch ) and use it on a applicator and it is removing the stain and it appears to be black but it will be a lot of scrubbing . I did shock before getting out the pad. I will post readings after checking water in morning but PH was 8.0 the other day . Chrlorine FC was at 5.0 but CYA appeared to be below 30 .Have not added anything else like Poly 60 yet . Thoughts -next steps

[gfritz1]

Tested chemicals - PH 8.0+ ,FC 7.2 CC .2 TC 7.4, Alk 110 ,Hard 120,CYA 60

[CarlD]

At first glance the obvious thing you need to do is get your pH down to the low 7's. Chlorine loses effectiveness as pH gets higher--rather rapidly!

I have troubles with your volume calculation. Unless your pool averages 6' deep I don't see how you get 23,000 gallons. For example: If your pool is 4' deep, you'd have 16000 gallons. You'd have to have half the pool as a deep end of 8' to get 23,000 gallons. Volume = L x W x D x 7.48, where D is the water depth and 7.48 is the number of gallons per cubic foot.

[gfritz1]

Carl my profile I is correct except it is a inground not a above ground .It is a 16x32 with a 8 ft deep end and also a set of steps off the side thus the calculation of 23000. I started lowering the PH last night and will check this morning . So other than lowering PH and brushing any other suggestions?

[CarlD]

OK, but your sig line says "23k gal AG pool" so I figured either the AG or 23K had to be wrong.

Ok: Looks like you're testing FC and CC with the 25mil line, and every drop counting .2ppm. Don't. Use the 10mil line where every drop counts .5ppm--it will save your reagents and you don't need anymore accuracy than .5. Most of us never use the 25mil line.

Once you get pH down, test FC again and CC again. Don't bother with T/A, CH or even CYA. T/A will be lower, no problem. CH is irrelevant with a vinyl pool--assuming it's vinyl. If it's not you can worry about CH later.

Then you're going to want to raise your FC to at least 20ppm and keep it there. You can use bleach or, if you want, cal-hypo powder. If your pool is hard-sided, not vinyl, cal-hypo's a good choice because you'll want to get CH to 200-40ppm eventually. Do not use Di-Chlor powder or Tri-chlor tabs as both add CYA and yours is high enough.

Once you get FC to 20ppm, you'll want to follow the standard algae fighting procedure laid out here: Test FC 3x a day, especially after the sun passes in the evening, and add chlorine to bring it back to 20ppm.

You'll want to vacuum the dead algae to waste once a day, and brush the walls and bottom once a day as well. You'll lots of POPP--"pool owner patience and persistence".

If you use bleach, 1 gallon of 8.25% adds about 3.5/3.6ppm of chlorine to your 23k pool. 1 gallon of 6% adds 2.6ppm of FC. Adjust accordingly. Never can remember exactly how many pounds of Cal-hypo powder you need to increase FC.

[Watermom]

gfritz1,
Click on the "edit my signature" tab in my signature below and you can fix your signature line.

Also, I believe Carl meant CH level 200-400 in his post above instead of 200-40!