well the question now is if this is safe for the fish in there? You said it formed where the sun was the strongest, moving it to a shaded area should help prevent it then I would think. Plus goldfish will not live in a metal tank if the sun is on it, the water will heat up way too hot for them and they will die. Goldfish like cooler water. Do you have anything moving the water around, an aerator-something to add oxygen, like a fountain or bubbles?
