you can use the fir/pine plywood.go to your local sherwin williams paint dealer and get some "Tile clad II" 2 part epoxy paint...i like to use black;but white is ok too.just make sure that you give it 2 coats about 24-48 hours apart.
I would paint it with either an epoxy paint as loha suggested or a waterproof/mold resistant paint. Also, I wouldn't paint it white, as it will get dirty and look bad.
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55 Gallon Tank (Display):
-Community Fish (Angelfish, Blue Gouramis, Gold Gouramis, Peppered Cories, Pleco)
40 Gallon Tank:
-Pseudotropheus Cichlids
20 Gallon Tank (Planted):
-Pseudotropheus Cichlid (permanently injured)
20 Gallon Tank (Planted):
-Swordtail Fry
10 Gallon Tank :
- Betta
10 Gallon Tank (FOWLR Saltwater)
-False Percula Clown Fish