I use 2 T8 shoplights over my 80 gal & it is fine for medium.
Definitely don't go for the cheapest .... you want:
1. An electronic ballast - these are totally sealed & won't rust & die in a wet environment, plus there is no fluorescent hum., and much lighter.
2. Get one with a good reflector so the light is directed downwards.
I would get Daylight T8's as that is the most cost effective in terms of light output vs. watts & $$.
I took the shoplights apart & mounted the reflectors & lights in the canopy, and wired the ballasts outside. <There is a limited length of wire you can use to wire a ballast to the holder .... I use the same wires that came with the shoplight, just moved things so the ballasts & all wire connections are outside of the canopy. <No water & electricity mix ...> All wire junctions (including the 110V in to ballast) are done inside a plastic (outdoor) junction box.
In theory - you are supposed to replace the endcaps (tube holders) with waterproofed ones. I left the original ones on, and they have been fine for over 5 years. If they start to rust, I would replace them with waterproofed ones as needed.