[pspringer]

i have 2 65W 50/50 bulbs that i currently use, how many hours should the lights be left on each day?

[BLKBRDTA]

I would say 10 hours. You could go more a day, it really depends on coral, but your risk of algae blooms also increases.. Which ultimately will bring your lighting schedule back down anyways.

If you are currently running a FOWLR, lighting does not have to be intense and spectrum focused. If you are running a reef system, your lighting must yield greater PAR readings therefore be more intense. At least 3.0 - 3.5w/g is a good rule to go by, again, could go more.

2 x 65w = 130w / 75g = 1.73w/g. FYI.

[pogodzib]

Since 2x65w bulbs over a 20" tall tank isn't very much, you'll probably want to be in the 10-12 hour/day range, depending on your corals. Certain corals may not need the lights to be on that long, but others won't be able to thrive no matter how long those lights are on. If you are sticking with the lower light demanding corals, such as shrooms, dull colored zoos, polyps, and softies, then 10 hours per day should be plenty fine. If you have some LPS, you may want to go a little longer and keep them higher up in the tank.