ooh a sump... Im trying to make my first saltwater 20 gallon aquarium, and Im not sure what equipment I need, though I've been told not to get a protein skimmer and sump is optional, do u know a good filter to get?
What are you trying to put in the tank? That determines a lot.
For a 20 gallon nano, you could do a canister filter probably.
Live rock is the best filter overall, but it cant do it all alone.
You want at least one type of mechanical filtration (something that separates large particles from the water) like a sock filter, power filter, or cannister filter.
Multiple type of chemical filtration - this can be either chemicals that change nitrogen/ammonia levels, or the protein skimmer is considered chemical filtration because it's removing dissolved substances in the water.
and finally, your biological filtration. Live rocks, nitrifying bacteria.
Keep in mind a smaller tank is a lot harder to manage because water levels get fouled quicker in less water volume, so filtration is going to be super important for you.
The general rule is, buy the biggest tank you can afford. Costs don't start to skyrocket till after 50-55 gallon tanks.
Both Petco and Petsmart are having 1dollar / gallon aquarium sales for another week or so.