i have a 30 gallon tank, with 5 fish, 2 crabs and about 15 lbs of live rock, how often should i do a water change and and whats the max number of fish i can have..is 7 to many???
Stocking rule of thumb is 1 fish per 10 gallons of tank volume
As far as water changes, you should be aiming for at least 10% a week (or 20% bi-weekly) but with an overstocked tank, you may need to do a larger percentage - such as 20% per week to keep water parameters in check