LR is the one that normally eats the nitrates converting to nitrogen that realeses through gas exchange in your tank. One more question, what type of sand bed do you have? This also affects your nitrates removal. I normally feed every 2 days. My current set up is Deep Sand bed, with bio balls, and lots of Live rock. So the bio balls convert amo to nitrites to nitrates then the sandbed/LR should get rid of the nitrates.

Phosphates on the other hand (usually the algea problem) is attributed to feeding, but you can not compltely stop feeding, so you need to remove those nutrients (phosphates) some how. Thats why alot of people set up refugiums to grow macro algea that eats this nutrients so you dont get bad algea in your main display. Do you have a refugium? If not I recommend a refugium or a phosban reactor/sock with phosban in it.

Good luck with your battle!

PS: About your clean up crew dieing, if the snails flip over you need to reflip them since they can not flip themselves.