Adding a 10 gallon tank to my establish 20 gallon system

[allenb94]

Hey guys, I have a question about a project I am planning out.

I have a 20 gallon long nano FOWLR plumbed into a 10 gallon sump that has been running fully cycled for about 3 months. I have about 30 pounds of live rock, 40 pounds of live sand, and a skimmer ranked for 50 gallons. The only live stock in it right now is a firefish, a watchman goby, and some snails and shrimp. As much as I like them, I'd definitely enjoy keeping a fuzzy dwarf lion fish more. With that being said, I would hate to get rid of my gobies and shrimp as I've gotten to enjoy the little guys.

If I were to plumb a spare 10 gallon tank I have laying around into my sump and move 10 pounds of live rock and sand into it (essentially just tacking on a 10 gallon tank into my established system), can I avoid having my tanks cycle and put fish immediately into it?

Thank you guys so much! RC has been such a great tool these past few months with setting up my 20, first time posting though!