Brown stains on plaster

[nedmitchell]

Photos attached. Pool was replastered ~5 years ago and brown stains have gradually appeared, but gotten significantly worse this season. Pool chemistry is very closely monitored and maintained using a TF-100 and PoolMath.

FC: 3-6
pH: 7.8 (Muriatic acid is added a couple times a week to combat pH raise due to SWG)
TA: 70-80
CH: 325
CYA: 60-70
Salt: 3200

Brushing doesn't affect the stains. The plaster is also pitting in some areas, not sure if that's normal behavior a few years after replastering. I have always suspected the stains were somehow related to pH balance as that has been the most difficult to control.

One pool company recommended drain and acid wash, but they couldn't offer any explanation for what the stains are. If that's the right thing to do, I would plan to do the no-drain acid wash process posted elsewhere on the forum. Any thoughts? Appreciate any insight.

 

[Texas Splash]

Mitch, are you on a well? Have you tried rubbing the stanined area with a Vitamin C tablet? If it helps, that's iron staining. If not, try rubbing a chlorine tablet on the stain, but don't let it just sit. Move it every few seconds (organic stain). Besides the salt, muriatic acid, or perhaps an occasional round of liquid chlorine, has anything else been added to the water?

Is the staining limited to the drain where debris might tend to settle, or does you see it anywhere else?

 

[nedmitchell]

Not on a well - on city water. Have not tried vitamin C. Haven't tried rubbing chlorine tablets on it, either. Pretty difficult to access the area as it's at the bottom of the deep end but that could be attempted.

CYA and baking soda have been added as needed on startup to get the water in balance. Had the water tested at the pool store this summer just to double check, they said it was in balance but said phosphates were high and recommended adding phosphate remover - didn't pursue that based on the general sense on this website that phosphates aren't a problem if everything else is kept under control.

The stains are mostly concentrated in the very bottom of the pool, in rings, as if something has settled there, but the pool gets cleaned so often that there isn't much debris down there.

Thanks for the input!