lighting a 55 gallon acrylic tank

[trdbird7]

can anyone tell me what i need to light my 55 gallon acrylic half hexagon tank. its been running for about a month with live sand and some damsels. i would like to get some live rock soon and eventually start corals. what kind of lighting should/could i get that isnt going to kill my wallet? is a 250W 10k MH with batwing reflectors and 110/120 MH ballast be ok? please someone tell me what you think!! also what does RO/DI mean???

thanks

[HI SALINATY]

I am not real shure about the shape of your tank, but if it is a hex i would go with a halide (maby a pendant) but i would try a 20k bulb or you will need some actinic lights.

uoy could also go with a 400w mh

As for ro-di reverse osmosis and deionising are ways of water purefying