What can i have in a saltwater tank?

I started with a 10 gallon tank and quickly realized my error. The water volume is so small that it is nearly impossible to maintain water quality where it needs to be. I now have a 30 gallon reef with a 10 gallon sump, skimmer and 4 x 39W t5 light. I also use a powerhead and HOB filter for flow. And it is doing very well. I also have a 30 gallon FOWLR(fish only with live rock) tank with a canister filter and the standard light that came with it. It is also working well, So, you can do a lot with 30 gallons, but it takes experience and planning to be successful. Believe me, you will be much happier if you spend weeks or even months researching online, talking to pet stores and other hobbyists before you jump in.

1. you need more research, a 10 gallon is not suitable for clowns, or nearly anything.

2. research nano reef since this is all that can be done in a small tank

3. small means anything under about 50-75 gallons when you are talking about salt water and over 100 gallon is better for most saltwater fish. Only reef tanks, and small fish in a FOWLR set up do well under 100 gallons. Under 30 gal, is considered a mini reef or nano reef. and smaller than that is called a pico reef.

4. your light is nearly useless and no where near the intensity necessary for corals/liverock etc.

5. if you do the research a 20 gallon long would make a nice mini/nano reef tank, but again, almost no fish, certainly no large fish, no anemone, no starfish (there's a few that are small that might be ok) and you need 4 times as much light.

6. yes a freshwater filter can be used for circulation mostly, but it won't be nearly enough water flow and you'll have to add circulation pump(s) or another larger filter. you want about 20-25 times the tank volume in total flow/GPH.

Most saltwater begginers start of with at least a 100-125 gallon tank, You need to research more. Go to www.liveaquaria.com and go under saltwater begginers fish.