i personaly would not paint the inside of a tank. painting a few tubes or accents im all for and i would use fusion only. the only other option i would even consider is pond armor. problem is when it drys its a brownish color. you might be able to find similar stuff that comes in different colors but im unaware of any. search the diy section theres lots of people using similar products on there plywood tanks. theres alot of know how on this site. good luck to you!