I would recommend that before you do any water changes, get an ammonia test kit. Test for ammonia. If ammonia is above about .1 ppm
, you should probably do a 20% water change. If it is way above .1 ppm
, you should do as big a water change as is necessary to get it under .1 ppm
. Of course you shouldn't do more than about 30% at once. So if you are at .2, you should change out about 60 % of the water, but over 3 20% water changes. This will allow you to bring the ammonia down without stressing the fish more than they are being stressed already.
The reason I think you should test is that your aquarium is large, and you have live rock. Sometimes you won't see ammonia get very high in situations such as yours.