I've just taken over the care of a four year old fiberglass pool (9000 gallons) with a SWG. Its water is always clear, but it has had black algae spots for a month and now I'm seeing possible mustard algae spots too. I read all the pool school articles, then bought a DPD kit and tested the water. The results are so bad that I don't know where to begin. For starters, there is zero CYA. My husband (the previous caretaker) tells me that he has NEVER added any. There is also zero FC even though he set the SWG at 100% output three weeks ago. He was running the pump just four hours a day. Starting yesterday, I set it to run for 8 hours daily. I also noticed the SWG "inspect cell" indicator light was flashing. Last night I removed the cell, scraped off the deposits and reinstalled it. I reset the indicator light and this morning it is not flashing. If the cell is okay (hopefully) what is my next step? The salt level is too high (3900 ppm) but should I add CYA before adressing the salt problem? Should I add bottled chlorine now or wait to see if the SWG can produce enough to kill the algae? Additionally, the pH and TA are high because of the hard water in our area. My husband was adding a pint of muriatic acid almost every week.
9000 gallon IG fiberglass pool with SWG
1 HP pump, cart filter, 100 gpm flow rate
TA: 250 (pool store says our hard water causes this)
TC: Less than .5