Katy wrote:Thank you, This might work... Because it is a transparent green. It looks like it would be clear. Except it's a light green. As far as i know all that he put in it was algaecide.
Some algaecides contain copper. Look at the ingredients on the bottle to see if it mentions copper sulfate or anything else with copper. If you don't have the bottle, but remember the manufacturer and brand, then we can look up the MSDS to see what is in it. You can also have your water tested at a pool store for metals.
If you lower the pH and the water gets more clear, then it is very likely to be a metals problem, and most likely to be copper (though iron can be yellow that seen against a blue pool surface can look green).