its 2 month old for this 20 gallons, but the rocks were from a 10 gallon i had that is about 4 month old. Everything seems to be doing great and growing faster than i thought, especially the pom pom xenias. I have 4 fish, yes i know thats too much but they are all 1 inch or slightly more except for the new blue tang i added. I shouldve never bought it from a shady looking fish store that barely has a clean spot to walk on. Introduced some new ich as well. Had to remove all the fish and put him in my 7 gallon bucket qt. what do you guys think of this tank so far?