Why do I get a yellow percipate when I add ph increaser to my swimming pool water?

Question

My ph is low, 6.6 or so when I add sodium carbonate to my pool the ph increaser, turns a yellowish and I get a film on the top of the pool that falls out usually within a few hours, yet my ph does not increase much if any. I have a low cl level too.

Answer 1

Is there much iron in your water? That would explain the observations. The pH does not increase because the sodium carbonate is being used up to precipitate some insoluble chemical like iron(III) hydroxide.