What is causing this staining? Grey Mottling?

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dariushd

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May 26, 2017
70
West Hills, Ca.
My plaster pool is about 12 years old, we've been in this house 3. The previous owners I believe either acid washed or repainted the pool surface before we bought the house. I have been noticing this discoloration more lately than ever before, and am not sure what it could be coming from. I've read a bit the thread on grey mottling, but I'm not sure this is what that is since the plaster is at the very least 3 years old (if they resurfaced it) or more like 12 years and is not new plaster. I did not notice this level of discoloration when we first moved in.

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I just ordered the Taylor K2006 and should have it in a few days, I'll post new results then, but my CYA is 200 or so, and as I consider a pool drain, I want to see what I can do about the plaster stains as well. I had been using Clorox pucks in an offline feeder that has algaecide (copper) in it for maybe the past year, and I've only recently learned copper can stain, but I did a copper strip test that came out negative for copper in the water.
Both my chlorine numbers are about 5. I am waiting for the chlorine to get down to 0 to either drain, or *possibly* retry BioActive one more time before doing a drain and refill (or paying $600 for an RO treatment).
My last water test fro Leslie's is from a week ago:
CH 400
CYA 200
TA 120
pH 7.5
Copper 0
Iron 0
TDS 1625
Phosphates 125

I had Phosphates at around 1000 for probably a year or more, and successfully sequestered and filtered it down to 125 about 2-3 weeks ago.
 
Your CH is high, so the gray mottling is probably calcium scale. The only way to reduce calcium is to do a partial drain and refill or use the RO treatment. Same for the CYA. Are you on water restrictions?

You can manage high CH by lowering the TA to 70 and keeping the pH around 7.2, and brush the pool frequently. Eventually the scale will dissolve.
 
OK, here are some photos from my underwater point and shoot camera. I usually get that yellow/green algae on these parts first, and wind up brushing the side in the shade probably 1-2 a week, is that normal? Is that yellow stuff gonna show up all the time (usually starts after a couple days after a brushing). I am fighting my CYA levels, of course, but I'm wondering if that yellowish green is always gonna be there for me ot brush 1-2 times a week, or if my chemistry is out of whack and the chlorine is doing nothing.
 

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While your plaster is at least 3 years or more older, and based on the pictures, I still think that the grey areas are from the original plastering process and are due to what causes grey mottling discoloration. You may not have noticed the grey at first, but I think it becomes more noticeable once you become aware of it.
The pool may also have some calcium deposits that contribute to the discoloration. Of course, calcium scale is rough to the touch, and can be determined by that.

The yellow/green may either be from "yellow or mustard" algae, or from iron depositing on the surface. Iron staining can be removed by chemical treatments and/or sanding.
But since the yellow is constantly reappearing, it is probably mustard/yellow algae, and is probably continually sticking to the existing scale and hard to brush off.
The grey discoloration is mostly permanent.

Pools can be drained for short periods of time. But do it when the weather is cool.
 
This is my most recent testing (Taylor k2006):
FC: 1.6
pH: 7.9-8
TA: 175-80
CH: 600 (my tap water is about 80)
CYA: 240
Saturation Index 1.05

I'll be doing an RO treatment today. So keeping TA at 70 and pH at 7.2 is ideal to lower the scaling discoloration, though it sounds as if this is a permanent gray mottling from the plastering. I honestly don't recall it being that bad when we moved in 3 years ago, but maybe so.
 
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Would it hurt my plaster to use a wire brush to see if I can brush some of this discoloration? It feels fairly smooth to the touch, but I'm almost positive this is not something I didn't notice when we bought the house 3 years ago, maybe it was there to some degree, but it seems much worse. The home inspector before we bought the place thought the owners had done a paint job or acid wash or re-plaster on the pool at the time, so it was definitely not so moddled before.
Would doing an acid wash help this out, with the water still in the pool (I just RO'ed the darned thing)?
 
dariushd said:
Would it hurt my plaster to use a wire brush to see if I can brush some of this discoloration? It feels fairly smooth to the touch, but I'm almost positive this is not something I didn't notice when we bought the house 3 years ago, maybe it was there to some degree, but it seems much worse. The home inspector before we bought the place thought the owners had done a paint job or acid wash or re-plaster on the pool at the time, so it was definitely not so moddled before.
Would doing an acid wash help this out, with the water still in the pool (I just RO'ed the darned thing)?
Click to expand...

you know what, I think this is copper staining that is making the plaster mottling look worse. What's the best way to test for it? I did not have any copper in my water, but I was using Clorox Blue tabs that have copper in them. Man, the things I didn't know. Any thoughts on copper stain testing and removal? It's almost entirely on the walls so it's hard to reach and to leave a vitamin C tablet to sit there...
 

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dariushd said:
you know what, I think this is copper staining that is making the plaster mottling look worse. What's the best way to test for it? I did not have any copper in my water, but I was using Clorox Blue tabs that have copper in them. Man, the things I didn't know. Any thoughts on copper stain testing and removal? It's almost entirely on the walls so it's hard to reach and to leave a vitamin C tablet to sit there...
Click to expand...

I'm day 3 into a SLAM, and the discoloration in the mottled parts of the plaster seem to be fading a bit. :)
 
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