canister filter and nitrate


habitual reefer
hey guys, can some one explain why using a canister filter, or a biowheel for that matter, can lead to high nitrates? i guess i dont understand why they are appropriate in freshwater and not salt water. is it because corals need lower nitrate than fish? is their denitrifying bacteria that turn nitrate to gas? arent water changes necessary anyways?

i have a 30 gallon with lots of rock and a canister filter (lfs guy and others told me i dont need skimmer) i plan on doing coral down the i ok for FOWLR and swap the canister for skimmer later?
a skimmer and live rock is the best filtration you can have for a salt tank. in saltwater if you have coral and inverts you need to keep the nitrates as close to 0 as possible cansiter filters do work in saltwater but they need to be cleaned frequently at least once a week.
Nitrates are fatal to inverts. Anything below 20 is okay, but if you go above 20 you start to see the health of your inverts suffer. Fish can tolerate much higher levels of nitrates (in the hundreds) and therefore high nitrates aren't really an issue in freshwater or fish only saltwater tanks. Canister filters and biowheels trap a lot of detritus and that detritus just rots in the filter and is re-released into the water, spiking nitrates.

Nitrates are converted to nitrogen gas (good) by anaerobic bacteria, which cannot live in biowheels or canister filters. Anaerobic bacteria live in deep sand beds and deep inside live rock. Since canister filters and biowheels don't provide the habitat for this type of bacteria to live, you tend to get a build up of nitrates because there isn't enough bacteria to turn it into nitrogen gas.

Skimmers physically remove waste and organic material into a separate container (collection cup) so the gunk doesn't get rereleased into the tank. With other types of filtration, you constantly have water moving through it, washing the crap back into the tank.

In short, a canister filter is fine for fish only, but if you want inverts (shrimp, crabs, snails, starfish) and corals, a skimmer plus live rock is the best way to go.
thanks for the info- if i remove the canister, add a skimmer but dont have a deep sand bed, i should be ok? frequent water changes still to take out any nitrates im sure, are nitrates organic, does the skimmer remove them or will they still float around in the water?

also, since i am now planning on removing the canister and using it on my freshwater tank, can i take the hangontheback filter that is now on my freshy and use it in a quarintine tank? obviously i know i will have to clean and cycle the sponge anew, but would it be an appropriate piece of equipment for that application?
A skimmer wont actually remove the nitrates,but it'll get the crud before it can break down and cause nitrates.Live rock will take of most of the biological filtration,since you dont have a DSB.
Biff knows her stuff and is right on, a good skimmer and about 50 lbs of live rock should allow you to maintain a healthy saltwater aquarium.