Looks like you almost have 1lb of LR
per gallon in that 46 gallon tank. Your 15lbs of base rock will eventually become LR
extremely soon. I wouldn't even use those filters if it were me.
Anyway, I think it is possible that they could be producing nitrates if they go "biological". If you really want to use the pads, I would rinse them out under tap water at least once a week to kill any nitrifying bacteria that may be living on it. The idea here is that you want your LR
to become your primary sources of biological filtration anyway...