Posting for a friend.
They have black spot algae. Pool is Diamond Brite (Concrete).
Numbers are PH 7.2, FC 5, CC .5, TA 140, CH 750, CYA 40. 17K pool.
They use 10% liquid chlorine, she normally pours 2.5 gallons in once a week. I've recommended that she adds 3 times a week 1 gallon each time. I've recommened she bring it to shock level (15), maintain it there and brush using a stainless steel brush to expose the algae. I showed them pool calculator, got the total she needs to bring it up to 15 for shocking and try to maintain it.
Pool also has what appears to be calcium deposits on the sides, brushing with the SS brush releases it into the water.
Thanks in advance.