You are just painting the outside? Pretty much anything will be safe once cured. However, for a long lasting job, some of the marine epoxy paints or a spar finish would be best around water.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.