In a previous post I was asking about black algae removal for my neighbours pool, my neighbour is nearly 80 and just had serious heart surgery which will take at least a year to recover from, therefore I am maintaining their pool. Blakej gave the excellent advice to shock over a number of days until it is gone (5 in this case), at this post
I did this and the black algae, some was over 2 years old, has gone from everywhere except on certain parts of certain the steps which are within 1 ft to 3 ft of the surface. I have wire brushed twice a day, used the the Pentair AlgaeGone holder to brush and rub tabs over it. In most places on the steps this worked well but in some places it seems the Algae grows back each night. My guess, and it is a guess, is that the black algae is so deep rooted that it continues to grow back.
I think and I could be wrong, most probably am wrong, that the level of chlorine near the surface is not as high as deeper in the pool, is my thinking correct or off track, or is it the UV being higher at this level?
So what should I do? Increase the level of shock chlorine? Decrease the pH to 7.2, I fear doing this as the pool is severly delaminated? Increase the level of shock and CYA? Drain the pool down below the level of the steps and put chlorine soaked rags on the spots overnight or what else? Or let the pool return to a normal chlorine level of 8 and increase the CYA to 75 and continue daily with the pucks?
Obviously it is getting very expensive in the chlorine area as a jug is over $4.00 from Walmart here in Honolulu. I have used many jugs, nearly $80 worth at present.
I did add acid to the pool based on poolequations calculations when I added the liquid chlorine.
The pool is 20,000 gals plaster saltwater pool, about 25 years old, they cannot afford to re-plaster at present, the balance is below:
FC - 40 to 35 (shock level) (Normally 8 as we have mustard/yellow algae issues in our area)
pH - 7.6 (obviously cannot check at present FC levels but that is what I started with)
TA - 80
CH - 400 (I know too high I will reduce it later)
CyA - 60 (Will increase to 75 once the shocking is done)
Salt - 3100
Borates - 0 (Dogs)
Temp - 82
CSI - -0.10 (approximate)
One other issue exists. I removed a really bad black algae area about 3 ft from the main drain in the deepest part of the pool, about 6 ft deep, and then a day or so latter it seemed to grow back. All the other areas around it that had black algae were gone. I scrubbed it with a wire brush and a tab and it seemed to go away but by the afternoon, it came back. I then put a tab on it overnight and it actually got worse. I am beginning to think this is not black algae but a spalding issue coming from the concrete below. It is hard to see if it is black or dark brown as the trade winds have kicked up and the surface of the pool is always rippling. The roots of the black algae may have grown so far down it actually got into the concrete and the rebar may be spalding. Any opinions on my thought and what might be done?
My neighbours are very happy at the current results as there was lots of black algae in their pool. I have not discussed the possible spalding issue with them as I do not wish to worry them for no reason. Should we be worried if this is the case, I think yes but I am no expert?