I'm thinking about starting either a 10 or 20 gallon nano sw aquarium (hopefully 20 gallon) & I have a couple questions:
1. I have a whisper canister filter (210 gallons per hour rate) would it be possible to use that on at least a 10 gallon nano tank instead of a power head?
It could work.
2. Is a RO system really needed, or could I just take the chlorine and other harmful chemicals out some other way?
You would probably be better off with one, but it's not necessary.
3. Could I use play sand for the substrate as long as there is no silicone in it?
An aragonite based sand would be better.
4. I have a light that has two 25 watt lights for the 20 gallon, and 2 15 watt lights for the 10 gallon, would either of those be able to give enough light for any type of coral/mushroom? (They are just plain lights, not the coral kind of anything, but I guess I could put the specific coral light bulbs in)
If you changed the bulbs and bought some for corals, certain mushrooms or other polyps may be ok.
Last but not least, what kind of fish/corals could I put in a 10 gallon or a 20 gallon?
Not much for fish, maybe a pair of clowns or small gobys.
Sorry about all the questions, I just want to do this right.