My pool guy patched some hollows in my plaster and attempted to acid washed my pool this spring and filled it up. He didn't do a good job acid washing and there were stains all over the pool and a ring around the deep end (the deepest part was clean where the acid sat but the walls were stained). To fix this he replumbed the heater so that it was not in service, removed all the chlorine, drastically lowered PH to 5.9 or less and put in Jack's Magic and some metal sequestrant. The stains got worse but after 12 hours or so scrubbing them with a stainless steel brush they mostly came off.

Unfortunately, mustard algae had set in because there was no chlorine in the water. I shocked the pool, brushed the plaster, vacuumed and cleaned all my DE grids twice. The problem I am having is it appears that the mustard algae has permeated the new plaster patches as they now have a very noticeable yellowish brown tint.

I have now balance the PH and hyper chlorinated the pool using Chlorox bleach. The chlorine level is off the charts and my cheap test kit can't register the ppm but it is very high. My CYA level is 40 and PH was around 7.4 before I put in all the chlorine. From reading this forum it appears that this is the preferred method to deal with mustard algae.

Is there any other advice on how to treat this problem? Another thought is that the yellowish brown stain on the new plaster patches could be from the low pH eating away the color off my stone waterfall and that color gets set into the new plaster patches.

Any ideas or help is appreciated.