Pardon the brief hijack but I have a question that is sort of aquarist related. I just purchased a 2nd hand 5 gallon tank from Goodwill and noticed the caulking is stained greenish... I soaked the thing in super hot tap water and 10% bleach. Afterwards I dried it with paper towels and this green stuff (malachite green maybe??) is STILL coming off on the paper towels, but is also still in the caulking. Is it safe to use this tank for a hospital enclosure for frogs or should I skip it?