Canister VS Sump

[ThomasLC]

I crack my canister filter open about once a month to clean the mechanical filters (sponges), but for my sump they say I have to swap the socks out once every three days?  What gives?

[HH Morant]

I think for a mechanical filter you can just clean it when it gets dirty enough that to impede flow. 

I have stopped using mechanical filtration in my canisters. That way I don't have to clean them as often, and they are much better biological filters because I don't clean them often. I have found that using 30 ppi foam in the canisters with zero mechanical filtration makes my water more clear. See www.aquariumscience.org.

[StevesFishTanks]

I use big prefilter sponges from jehmco on my fx4 and fx5. Like HH I pack the cannister with bio only. Mostly matrix and some crushed coral. I service the prefilters with every water change and only ever crack the cannister open every 4-6 months just to check on it. 

[OnlyGenusCaps]

Okay, cards on the table, I'm a sump-head. IMO canisters are overpriced and offer little improvement for the space. 

With that out of the way, Any filter will become a "biofilter" if left in place long enough.  We should really think of them as "bioreactors".  Socks are awesome!  The only reason to change them out is if they get clogged.  Otherwise you can keep them in.  I change mine once a week when I do water changes.  Why?  Because it is part of my routine, and then they work as mechanical filtration primarily.  I also rinse out my sponges at the same time. 

I think the "change our socks" paradigm comes from the salty side of the hobby.  @eatyourpeas can tell you about the experience in salt and the difference between FW and SW, but I think SW is dirtier, thus resulting in SW advice being to change out more often.

Sumps rule!!!  😈

[Aquatic Journal]

I think this comes down to two different things.

One your canister filter may be getting equally as dirty but you do not see it so you don't clean it. The sock in the sump is something that is easy to see and therefore you are more likely to clean it.

Two if you are using sponges in the canister and something like poly fill in the sump those will clog up at vastly different rates. I change poly fill every two days and a sponge filter once a month. 

So what are in each of the tanks, what type of filter sock you are using, and the size of the tanks vs the sump or canister would help answer that question.

[eatyourpeas]

I use canisters in my FW tanks, but they are all less than 12 gal., so a sump would be a stupid choice. I clean the coarse intake sponge with every WC, but the canisters themselves once every four months or so. They have a combination of sponges and ceramic bio-media.

I do have a sump in my SW tank. It is a 36 gal. temperate tank, so I had to rely on mechanical filtration since the BB took a couple of months to get established. It is a 5 gal. sump tank inside a 10 gal. tub. WC once a month, sump cleaning only once so far, tank has been running for almost four months. Still fine tuning flow, but the water runs clear and parameters are good. Socks are 50 micron and 180 micron mesh. Tank is stocked with about 30 fish, 16 anemones, a few crabs, clams, starfish, mussels, macro algae.

I have been exchanging notes with @OnlyGenusCaps and do not think I would ever consider a canister for SW. The critters produce an exceptional amount of waste.

Edited October 26, 2021 by eatyourpeas