Been trying to help my sister with her 16000 gallon fiberglass pool built in the 80s, she allowed it to get real bad full of leaves and basically a dark brown soup. So once I did the clean up, removing two years of leaves,with the water still dark brown I brought it to shock level for several days to kill anything that might have been living and growing in there. Once I got it pretty clear and allowed it to come down from shock, the pool developed brown stains all over making the pool water look greenish yellow even thought he water was clear. Figuring out it was iron staining with a vitamin C tablet, I followed the directions on the 2lb Leslies Stain Remover, bringing FC to 0 and PH to around 7.2 before applying.
One point of note is that when I tested the water for the first time for PH, after letting the FC go below 10, I got an extremely yellow reading, now I understand that this would be 7.0 or below, I believe below 7.0 cause it was so yellow. The TA was 30, so before I used the stain remover I had to add borax and some baking soda and was able to bring TA to around 150 and the PH to 7.2. This begs the question for future reference, how can I test lower than 7.0 ph with the phenol red so I can get an exact ph to plug into the caculator to add the proper amount of borax or baking soda? I have looked around the site and cant find the answer.
Well I added the Stain Remover, the entire 2lbs added a little bit more than it needed, and before my very eyes it started working on the stains, waiting 1 hour, then added Natural Chemistry Metal Free to as the sequestrant, (I now learned that is not a recommended one here). Waited 24 hours and backwashed. There are still some very light shades of staining left especially on the walls so I was wondering if another dose of the Stain Remover is needed now that its been 5 days and its still there, I have not added any bleach and have the FC still at 0. And I guess if I add another dose of stain remover, with it hopefully suspending the remaining iron deposit, I would have to follow up again with another dose of suquestrant. Looks like from what I have been reading you either have to replace the water or keeping adding suquestrant on a regular basis to keep the iron from redepositing on the surface since the sand filter will not remove it.
At first I could not figure out how the iron entered the water because we pull from the same city water supply and my pool never had stains and she has no heater or metal piping. My sister has a well pump with hard water, no softener, to water her flower beds and over the last two years she was running the sprinklers near the pool that eventually turned the concrete on one side of the pool yellowish brown. Seems the sprinklers were throwing hard well water into the pool too and it must have really built up then when I shocked the pool, which was never done before, it made the pool surface a very yellowish brown rustic color.
Any information greatly appreciated