I am surprised I still see people using LR and LS that still use "biological" filters. As long as the tank has cycled, you do not need this kind of filter. Your LR and LS are your filter! A filter will only break down waste into nitrates and raise your nitrate levels. Put on the CPR or similiar skimmer and lose the other filter. Your deep sand bed will have an anaerobic layer where bacteria will live and break down nitrate to free nitrogen which will escape to the atmosphere via bubbles. If you don't believe me ask someone else. There are tons are succesful tanks on this site that don't use biological filtration.