Yellow Stain on Plaster Patches

[poolese]

My pool guy patched some hollow 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.

Unfortnately, 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 yellow 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?

I am very concerned that the mustard algae has gotten established in the new plaster patches and will be extremely hard to eradicate.

[Looper]

Get yourself a good pool guy.

I'm not sure what is causing the patches to turn yellow. Is the yellowing specific to the patches and not the surrounding plaster? It sounds like it may have been a very bad patch. Are you sure it is not rust coming from behind the patch? That would be my guess. If it is, then it will get worse in the next few weeks and it will be obvious that it is rust. I have frequently seen embedded algae in pools with rust problems.

I am also unsure what "Hollows" are this guy was repairing? The only time I do plaster repairs is if their is a rebar rusting problem.

When I have a problem with embedded algae, I use 2 gallons of industrial liquid ammonia. They only sell it at commercial pool stores, so get yourself a good pool guy, but it will kill everything in the pool and more. Make sure chlorine is up as well as a low ph. It will send your PH level high but it is fixed after treatment with a gallon or 2 of acid. It will not touch the chlorine. The pool also needs to be closed for a few days till the ammonia is out and use a chemical mask when putting it in. Bad Stuff and expensive.

How old is the pool and has it ever been replastered?