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You may have evaporation without the hood on but, keeping it on is just raising the temp more by not letting the heat escape. MH lights aren't as bad with heat as everyone thinks, both my tanks run MH lights and I don't have any temp spikes during the day. If you want to stay with T5 lights these are good, 48 in. Nova Extreme Pro T5 HO Lighting Fixture - (6) 54 watt lamps | T5 Lighting | Lighting Systems | Aquarium - ThatPetPlace.com These lights will also work on tanks up to 100g if you decide to upgrade down the road. There are other options you could choose from this site Aquatraders - Guaranteed Best Prices on Aquarium Lightings + Free Shipping! as well.