I agree. It can be done, but bear in mind that it will cost nearly, if not as much, what a larger tank will. The tank itself is really the cheapest part of a SW
system. Counting livestock, we easily put about $1000 into our 20 and it was set up as "bare bones" as you can get. Read the links Mike posted. Keep in mind that a cycled FW
filter will do nothing but create an ammonia spike and start a cycle in SW
. It takes A LOT of diligence to keep everything alive in a 20 and like I said in our upgrade thread, I really wouldn't recommend starting so small unless you are very experienced and/or OCD like me.
What are you shooting for? Reef, FOWLR