OK I need some serious help for a serious black algae problem. My parents purchased a house with a pool several months ago. The pool was pea soup green when they moved in. Thanks to TFP and a FAS test kit I have managed to get the water crystal clear and all parameters back in range. The problem is the pool is approx one third covered in black algae. We have been brushing daily or every second day and keeping the chlorine at a slightly elevated level for at least the last month but it just does not seem to be clearing up or so it seems. Is there something else we can do or do we just persevere with the brushing and keeping the chlorine slightly higher. I have enough managing my own pool let alone the parents as well.
Pool is very similar in volume and surface to my own pool but here are the exact details.
Pool volume 50,000L
salt water with a salt water chlorine generator.
T/A: 120 (SWG booklet recommends 90-150)
Calcium:300 (SWG booklet recommends 300-350 for this pool surface)
CYA:60 (SWG booklet recommends 40-65)
Salt:5600 (SWG booklet recommends 5000-6000)
I know chemicals for treating black algae are not recommended but is there some way to get this under control.