Hate to be the bearer of bad news here, but you should really give up one of those fish. 22 inches of fish mass is hefty, even for a 75 gal you are pushing it with the meat lovers like you have there. Suggest returning at least one and trading for smaller specimen; esp. the 10 inch puffer.
Nutrients equal nitrates my friend. You need to identify the nutrient trap; likely the cannister or a gravel substrate; even wheels and trickle bio media are all highly efficient at converting to nitrate; factories indeed. The skimmer on the other hand, actually removes target nutrients before that takes place. A word of caution here: disturbing old substrates can release sulphide into your system causing far more danger to your charges than the nitrate; use common sense and make changes slowly. What you need is nutrient export; adding a second skimmer will help, an oversized unit (i.e. Euro Reef or Turbo Flotor) is worth the money, also do consider a remote sump planted refugium with deep sand bed; many have reported dramatic drops in nitrate with this method. Meanwhile, consider lightening the bioload to pinch at the source.
Nutrients equal nitrates my friend. You need to identify the nutrient trap; likely the cannister or a gravel substrate; even wheels and trickle bio media are all highly efficient at converting to nitrate; factories indeed. The skimmer on the other hand, actually removes target nutrients before that takes place. A word of caution here: disturbing old substrates can release sulphide into your system causing far more danger to your charges than the nitrate; use common sense and make changes slowly. What you need is nutrient export; adding a second skimmer will help, an oversized unit (i.e. Euro Reef or Turbo Flotor) is worth the money, also do consider a remote sump planted refugium with deep sand bed; many have reported dramatic drops in nitrate with this method. Meanwhile, consider lightening the bioload to pinch at the source.
