Hi all, haven't post in a while but keep reading when I can.
We took over a pool almost 18 months ago or a little more. First, it had black algae on the walls, not much, but it was obvious and present, but more important,
it didn't matter how many times we brushed (with nylon or metal), or if we raised the chlorine level (not to shock level though), the algae wouldn't dissapear.
The pool has some sort of pebble finish, but it is not smooth, so algae is able to "hide" intho those places where the brush can't reach.
So, the story is that we drained the pool (CYA leve was like 180+), we shocked the pool (normal algae levels), with the brushing and vacuuming process and in the end
it took 18 months (until now) for the black algae to come back.
It is back and much stronger as it was not possible to perform the shocking for a while and the pool was "very" busy all the time (many guests in and out for some months).
Black algae is worse and looks like a stain on the walls now. Very hard to get off. So finally we have the time and chance to do the super shocking level. The CYA was too high again, so pool has been already emptied out giving the following readings:
It is a SWG and it is an 11,100 gallon pool with a not that big sand filter (yeah, I know, bigger is better but owners will change it someday).
The pool calculator says the mustard algae is 19 but here are my questions:
1) Is mustard algae considered as strong as the black algae?
2) That black algae is very hard, so we are really considering in using double the dose and keep the FC at 40. How does this sound to you?
3) We will do as possible a two time check a day, with brushing, but the question here is: do we have to vacuum everyday? or just every other day?
4) We will back wash the filter also from time to time and keep the pump 24/7. Is this ok or the pump can be set at a different schedule? The pool is not that green, just a little for now.
Any advise will help.
Two other options were considered before, but they were to expensive for now:
a) Re do the pool with tile (small blue squares)
b) Acid wash the pool
Cheers to all!