Hi there. I'm new to this forum. It certainly seems to be the best one around after spening a lot of time trying to get a sensible answer from other sites.
Here is my problem, a brief history of what I have discovered and what I think is wrong. I'm really hoping I have come to the wrong conclusion.....
Problem: A light brown stain that is even all over the floor and walls of my fibreglass swimming pool - anywhere the water touches. It is like a plating has occured. No scrubbing removes it (so probably not algea), no 'miracle product' has had any impact. There are nometal pipes or otherwise touching the water. I've been good with keeping within recommended chemical levels.
A brief history: The only thing that moved the stain was a 15% dilution of hydrochloric acid. No elbow grease needed, just washed off. Excellent. So I put 20 litres (5.2 US gallons) in my 36,000 litre (8,000 US gallon) pool and after a couple of days on recirculate the pool looked as clean as it ever has. Excellent. Of course the balance was now wrecked so I slowly bought up the levels and made sure my Total Alkilinity, PH, hardness, sunblock were at optimum levels and only then added the chlorine. By this time algea was forming so I also added some polymeric algeacide (non copper based).
Within 24 hours the pool went brown again. Not excellent. My levels are as follows (as accurate as test strips can be):
free chlorine just below 10ppm
Hardness was tested at pool shop and okay, cyanuric acid a little high but not enough to cause an issue.
It is only the pool that is discoloured. I put a plastic milk container (it is a white colour) half in the water and this didn't go brown. If I rub the stain with ascorbic acid the stain comes off.
Answer??? Has the fibreglass just reached the end of it's life and has just become reactive to the water?
Any help would be great. I'm going nuts here and I don't want to keep spending money on a more fundamental problem.
Thanks anyone who can help.