We've had a long, hot dry summer, but finally got some rain last night, and I've got a minor algae bloom a few places on the walls and bottom.
I've used PhosFree for a number of years, and have essentially put an end to algae problems. But I hadn't used it this year since the water tested low at the beginning of the summer.
So I took a water sample in, and the store guy said the phosphate level was about 100, which was ok, and I didn't need to lower it further. But if that's the case, I wonder why algae is growing.
I'm sure I've used more chlorine than usual this year, so my stabilizer level is probably a bit high, but even so, it seems to me that after superchlorinating and vacuuming the algae to waste, I need to follow with a liter of PhosFree to take the phosphates down to near zero. (19k gallons).
Then, as I usually do, at the end of the season, drain the pool down about half way so that when refilled the stabilizer level will be back down to around 50. Then I have to check again for phosphates in case there was some in the fill water.
The alternative would be to do the big drain-down now, refill, and add PhosFree. But then I would be adding lots of chlorine, and stabilizer, during the final month of the season, and that's gonna screw things up for next summer.
Well, anyway, what I need to know is whether I'm right about needing to get the phosphate level down, to stop the algae from coming back. It seems to me if the phosphate level is low enough, algae shouldn't grow.