When I was using them (which I will again at some point) I changed them out every 3 or so days and washed them in the washer with Clorox(only a cap full) and rinsed 4 X.
try taking it off n let your LR n LS have a crack at them for a couple of days. your nitrates may just get lower. depending on how established your rock n sand is, it may be a better option.
also your protein skimmer may not be doing its job efficiently.