I have 125 gal that's about 2 years running.I do 30 per water change weekly i have three ac110 which i clean one a week,vacum gravel except under the rocks,question is when do you think i should take out an vacum under rocks .I notice when i lift one rock how dirty it is ..by the i have about 12 fish in tank average 7 inches , any anwsers would appreciate....