Equipment for a 20 long?

I'm assuming its a T8 (standard fluorescent) fixture. 60w is enough for the various low/med light corals (softies, morphs etc).
You don't need a skimmer. A hang-on one like a remora or something similar would benefit the tank but skimmers aren't essential on small tanks. Regular partial water changes is enough.
Many people say a pound of live rock per gallon but just get whatever amount makes the tank look good, gives room for flow and allows for various spots to put corals.
I like having a single powerhead in a small tank, personally I think the 6025 tunze nanostream (the lowest flow one) is great for a 20g.

TropicalNorth said:

I'm assuming its a T8 (standard fluorescent) fixture. 60w is enough for the various low/med light corals (softies, morphs etc).
You don't need a skimmer. A hang-on one like a remora or something similar would benefit the tank but skimmers aren't essential on small tanks. Regular partial water changes is enough.
Many people say a pound of live rock per gallon but just get whatever amount makes the tank look good, gives room for flow and allows for various spots to put corals.
I like having a single powerhead in a small tank, personally I think the 6025 tunze nanostream (the lowest flow one) is great for a 20g.

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+1 to all! The Tunze would be a great choice.

The number of powerheads depends on the type of filtration you're using. If your filter is turning a significant volume of water, you may not need any powerheads. If you use a power head, give some thought to one of the types with the rotating nozzle to vary the flow pattern in the tank.

I would suggest using a protein skimmer. Those are always a good idea, and will give you some margin for error.

The amount of live rock you will need depends on how you want the tank to look and the type of rock as different rocks have different densities and 20 # of one type is not necessarily equivalent to 20# of a different type.

4 15 watt fluorescent bulbs should be sufficient. The next step is to get the right mix of spectrum. I'd suggest two 10000K bulbs, one actinic and one daylight (anywhere from 5000 to 6700K) as a good basic mix. You can certainly vary that depending on what you ultimately decide that you want to maintain.
Good luck,
Mark

Actually, the number of powerheads should more so be determined by the animals that are kept. Most filtration devices just don't provide nearly the same flow as a good, dispersed flow powerhead, like Tunze. I usually omit any flow included by any filtration, since the actual volume will be small by comparison--assuming there is any external filtration to begin with.

i seen some ware on michiganreefers.com ware a guy made a sump / fuge out of a AquaClear 70 HOB filter for a small saltwater it was cool

blue2fyre said:

Ok so say I wanted to just keep a pair of clownfish and maybe some other very small fish? How many powerheads would be needed for that type of set up?

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Actually, I think TropicalNorth's suggestion is perfectly adequate for what you want. That particular pump is very small and features a high flow rate at 660 gph. A very good powerhead, IME, and I also highly recommend it.