Here is a 700 gallon tank that I am hoping to raise golden shiners in. I just found out about the zinc toxicity to fish. Should I drain and paint the interior or do you think algae growth along the walls will prevent zinc contamination? Thanks

Use a heavy plastic liner?

I agree John. I think pond liner would probably work best.

You don't think the paint would work or you just think a liner would be easier?

I'm not sure where to get a liner locally.

Might be easier to just get a plastic tub. It's hard to adhere paint to galvanized steel. I was referring to making a liner out of a couple of layers of 6 mil plastic sheeting available at lumber yards.

I have decided to pull the tank out, clean and dry it, and coat the inside. I now have to decide what to use. I am torn between Pond Shield epoxy paint (http://www.homedepot.com/p/Pond-Armor-Po...-QT-R/203886501) and Rubberseal (https://www.amazon.com/Rubberseal-Liquid...rds=pond+shield) at 1/4 of the price. I have concerns about whether either of these will adhere well.

Money aside, which product do you think would be better for the job? Thanks

I don't think galvanizing is toxic until it starts to oxidize and even then not that big of a deal. I would be more worried about the bottom of the tanks rotting out.

The Romans used lead pipes too.

"The free zinc ion in solution is highly toxic to bacteria, plants, invertebrates, and even vertebrate fish"

https://en.wikipedia.org/wiki/Zinc_toxicity

I would prep the surface according to the paint mfg recommendations. If I were doing it, I would pick the epoxy paint.

If you have to add salt to the water for any reason (stimulate slime coat, remove external parasites or any other reason) that will hasten the reaction with the zinc if it isn't coated.