Most latex paint should be fish safe after giving it time to cure. In other words, paint it and give it time to sit before putting fish in (which you should do anyway for the health of the fish). I would probably sand the tub abit to rough up the finish, and then apply a couple good coats of paint. Let it sit for a couple days to get good and dry, fill with water and let sit for a couple weeks. You can go ahead and add your dechlorinator and some bog or water plants.

Here is a link that might be useful: My Backyard Gardens

Great! Thanks! I'll try that. I figured it would be more complicated than that.

also, tricker, they sell water lillies, has fish and plant safe paint for cement ponds, you could e-mail them and ask if it would adhere to porcelain. just from what i know about paint in general, nothing will stick to such a slick surface, you will have to sand it first, no matter what type of paint you use. donna