How do you know it is time to clean a sponge filter?

[Pepere]

The bubbles will be bubbling up whether water is still flowing through or not.  How do you decide it needs to be cleaned?

[Andy's Fish Den]

If it is one of the finer sponge material ones, you will be able to tell a lot easier than the co-op ones, but you will not be able to see the holes in the sponge. Or, you will be able to see dirt and detritus building up in the pores of the sponge. 

[Cory]

For me, with our sponge filters. I clean them out of "it's been a long time, I should probably clean that" to actually clog a coarse sponge filter is pretty unlikely. For most of my sponge filters I go at least 6 months between cleanings, outside of major tank overhauls where I'm kicking up a  lot of stuff.

[Theplatymaster]

at this point i clean out my sponge filter for 1 reason;

raising fry.

i will squeeze out the sponge into the breeder box for micro-organisms for the fry to eat.

otherwise i just leave the sponge filter in, no matter how dirty it is.

[Pepere]

I suppose a possible test is to raise it up so that the lift tube extends about an inche out of the water to see if it still lifts a flow up that high.

I have some fine double sponge filter that suction cup to the wall and I find that they will raise up about 1 1/2 inches when clean.  

The airlifts for the under gravels lift to about 2 inches above waterline…

[Bev C]

i have both canister filter and 2 sponge filters in my main tank when i upgrade to the tank i have now and the canister filter i missed my sponge filters so i added sponge  back  plus the extra sponge helps to ,,, and gives more hangs out for my pelco and snails plus  one of my sponge  is for emergency use if i need to start  new tank ,, I have sponge in my shrimp tank too 

I clean mine once a month or when needed ,the one in the shrimp tank i can go every two months in the shrimp tank they do a great job keeping it clean ,, and i do not clean in my main tank all 3 filters at the same time  i rotate them 

Edited March 20 by Bev C

[rockfisher]

I have some of the fine sponge filter and some of ACO filters. I have a loose schedule to clean them. I clean the fine every 7-10 day. Now I can do it sooner if needed which with the fine ones can happen. I do the ACO ones once a month. I agree that I don’t think you can clog one in normal aquarium use. If there are particulates  you can floating around or stuff collecting on the filter that would be my sign to change if I didn’t have a schedule.