what paint?

[Meefloaf]

this vid for idea's How to make a waterfall (rainforest theme) - YouTube

had a look around and people say use pond sealant but to make sure it is okay on polystyrene, if you've not made it, pond foam and silicone, this guy built a waterfall, might be worth giving him a line http://www.frogforum.net/vivarium-te...ew-tank-2.html

[deranged chipmunk]

you can use a clear two part epoxy to seal it with. they normally sell it in hardware stores with glues in the u.s. it will dry very glossy, but you can sprinkle some fine sand on it while it is still tacky to cut down the shine.