Put some micro blue legs in there and that should help a lot. You may want to also consider switching to some Tonga branch. IMO that helps circulation by allowing for an open LR architecture. The micro blue legs will also help minimize detritus buildup and will scavenge any fatalities you have. That's a pretty aggresive water change schedule. Try checking the alkalinity of your water change water to see if its low. If you are using Oceanic that may be the case.