alright man, that all sounds great but w/ a twenty gal tank, 10 lbs of live rock should clean you tank all u need, you dont need a filter, nevermind an undergravel one, and the undergravel filter totally doent work w/ live rock, as for the damsels, i would suggest acclamating one or two at the most at a time, and wait a week, also when acclamaiting them leave them in the bag for 15 min in the tank, take the fish and water and then slowly add about a cup of water to it about every 5 minutes, and finally when the water doubles in size drain the bag into a net and place the fish's in the tank,
if your still reading this, remember some fish just die
