That aquaclear will not be able to handle your bioload. How often do you change out the media in that?
I would keep up with the water changes until you can come up with an alternative. I would suggest getting an overflow, sump and a decent skimmer to go along with it.
How much are you feeding daily?
Also, are all of your fish accounted for? Even dead snails can cause your water quality to go out of whack.
Wet/dry converted into sump with a Bubble Magus NAC7 cone skimmer, MAG7 return, 200 micron filter socks, Vortech MP40w + two returns for flow. Current Sundial T5 + two retro Icecap T5's (6 bulbs),