I have an above ground pool - approx 17,000 gallons and am having never ending problems with metal staining on the vinyl liner - have used the ascorbic acid test which quickly removes the stains but unfortunately only temporarily. Have not been able to determine the source of the metal contamination - have tested the city water used to fill the pool and that showed minimal iron and copper, do not have a heater, have a Hayward DE filter (almost 20 years old) and pump - all other piping is plastic. So, I follow what I have found to be the directions for removing the stains (along with the metals) but the stains re-appear within a few weeks. Does anyone have a good quantitative measure on exactly how much metal sequestrant to add? I have been using Metal Free (1 liter treats 20,000 gallons) but stains re-appear once the pH rises above 7.2 and the chlorine levels are about 3.0.
The procedure I have followed is to add ascorbic acid at rate of approx 1/2 to 1 lb per 10,000 gallons and watch for stains to disappear - pump is run 24 hrs. Once stains have disappeared, I add the Metal Free (this time added a total of 2 liters) and let the pump circulate. I have no available chlorine at this point due to the addition of ascorbic acid and will start to add chlorine slowly after 24 hrs. I will continue to watch my pH and slowly adjust upward. I have been told no shocking for at least 2 weeks. I have used this procedure repeatedly, the stains disappear for a short time only to return. Guess I am looking for a more permanent fix to this problem - this is very frustrating! I would understand some of this if we had well water but that is not the case. Any suggestions will be much appreciated. Thanks.