I've been keeping freshwater tanks for about 5 years now and have been wanting to do a small saltwater tank. I have a spare 10 gal. and a spare 20 gal. tanks . I want to set up the 20 gallon as saltwater, I have a hang on filter and lighting for it .what type of other equipment will I need for a small tank or is it beter to get a larger tank for this? Also will live rock or corral do good in a smaller tank? A lot of bigger saltwater tanks I"ve seen have a sump system could I use the 10 gal. as a sunp on the 20 or would that be overkill?

small or nano) tanks can be just as beautiful as bigger tanks. however,the lower water volume means one have to be more diligent in husbandry as parameters shif can be quick.

the usual parameters like salinity(due to eveporation),temperature swing will have to be catered for.

and yes u can use the 10 gallon tank as a sump as there is no such thing as an overkill in this matter.

have fun.