Canister filteering for marine/reef tanks.

A well set up canister out preforms live rock easily, but it is work to keep it clean and set up.
First up where it picks up water to take to the canister, set it along the top of the tank just under your water height, say 1 inch of water above it, that will allow more oxygenated water to enter your canister.
Use conduit elbows and straight sections perforated with a drill but I use an angel grinder to perforate it for the area along just below the waters surface.

Okay, for over that perorated section of conduit that sits into the end so it can come out easily with fingers only going into water at one or so inches to take it out once pump is turned off.
Make a few socks open each end that fit over that conduit section with a relatively loose fitting and a rubber band on one end and a wrap around rubber band the other end, the rubber band will last weeks let alone for two days till the next time you take that section off and clean the sock.

Cut section of dacron/filter wool that goes around that perforated conduit section with a little extra making it loose, run silicon along one side, fold over and push down with silicon between the dacron, let it sit for an hour and now you have an open ended sock to put on your perforated conduit.
I would wrap two on at once to stop anything from getting to your canister bar water.
With in the canister, if water comes up from base and if no sections with in that will hold media, make a full sized base out of egg crate supported up say one inch, cover with mesh to stop media from going through, cut two pieces of cardboard the internal width of your canister and internal height, sit in canister, start filling canister with course calcium based media in the middle section and fine on each side, fill it evenly as it goes upwards.
Take out cardboards, once up and running for a couple of weeks, the middle section controls to nitrate, the two sides will reduce the nitrate!
Its up to you, which is most important out of the two types of media to make larger in volume!
Never have they failed with building up crap or not reducing nitrate in the tong term due to fine particles of rubbish reaching the bio media like near all media used by reefers, including the worst of all, live rock!!