Well Matt,

That's not true, unless u use cheap china made quality product as filtration layer.

Try Hydor canister or Tetra canister, replace the carbon becos carbon absorb iron, and some minerals required by coral, also carbon tend to give back once it is full. Just replace it wiv bio ring, better quality which can absorb more bacteria.

Try the JBL product.

For nitrate in your tank, u can always use the JBL test kit to keep the water quality in control and at acceptable level.

Well, perhaps u shud perform quality cleaning of the canister as well, this will ensure it is keep in top form and avoid blockages.