wow thats really slow how many water changes to do do a month?

i got a black bullhead for the bait shop yesterday. i put it in my 90 gallon with some small festae's. i was just woundering how fast do they grow. he rocks will eat right out fo my hand and only around 2 inches long. thanks Jeff

First Iam new to this site been reading some of the forms for a couple days now so far I like what I see. Iv been keeping large south and central american cichlids for ten years now and Iam looking for a change. I have a 75(us) gallon tank running and i have 3 sunfish in it now i need a catfish ...