In ground gunite pool stains

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mattbuff5

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Jul 30, 2013
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I am helping my in-laws who purchased a house in Ft. Myers, FL. The pool was built with the house around 2005. There are either blotchy stains all over the pool or the entire surface is discolored as I don't know what the original intended surface color. I have attached pictures for you all to see. FYI - in the pictures of the spa area, the darker spots are just where I was scrubbing and the lighter is where the water drained and the surface dried.

Imgur: The magic of the Internet

As of now the pool is maintained by a pool service with sanitation provided by dichlor pucks. This is what I have done so far.
1. Tested the water with Taylor 2006.
FC = 10
CC = 0.5
PH = 7.7
TA = 110
CH = 350
CYA = at least 110-120 as the comparator tube only shows marking beginning at 100
Water temp = 74

2. Since the test, I've removed all dichlor tablets, poured in 4 gallons of 7% clorox and started to drain water to replace 70% of the water to bring the CYA down.

While I have the water down I started looking at the stains. I've hit some spots with a dichlor tablet and hard bristle brush but didn't notice any change.

I don't know the exact surface finish, but it feels like some kind of exposed aggregate finish.

What are the next steps you all suggest to work on the stains?


As a side note, I'm trying to convince them to switch to a SWG but the pool service lady is saying SWG won't work during "rainy season". Another concern is when nobody is here for; potentially, 2 months at a time during the summer months. I've used the TFP SWG method for 3 years at my home fiberglass pool but I am there all year and have an auto-cover.
 

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Those look like iron stains. Try rubbing some crushed up vitamin C tablets in a sock on the stains for a few minutes and see if they start to clear up. I bet they will. You probably just need to do an AA (ascorbic acid) treatment and those stains will be gone.

The treatment consists of:

1) bringing pH down to 7.2
2) letting the FC drop to near 0
3) adding a generous amount of AA powder (I'd try around 5 Lbs.)
4) adding 2 bottles of Metal Magic sequestrant
5) slowly bringing the FC back up to normal levels
6) add a maintenance dose monthly (about half a bottle) of MM sequestrant to keep stains from returning

You might want to add a bottle of Polyquat 60 algaecide when the FC is near 0 to prevent algae from starting. Plus a good thorough brushing wouldn't hurt either to break up any possible biofilm from getting started. When you start to add the chlorine back in, you will find that it won't hold for long because it is eating away at any of the remaining AA left in the pool. You will go through quite a lot before it starts to actually hold. You will probably be adding it as frequently as when you do a SLAM, however, you don't want to get anywhere near SLAM chlorine levels because the stains could drop out of solution and back onto the pool surface.

I did mine last August and my pool still looks great with just the maintenance dose of MM sequesterant added once a month.
 
If you think it's copper, you could try the dry acid test and see if that lightens things up. I don't have any experience with copper stains though. Hopefully, others will chime in with some good advice. Swampwoman is the TFP metals expert here. Hopefully, she'll see this thread.
 

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