Correct, I've never cleaned it since I set it up because I didn't find any suggestion from the manual, so I waited until it shows some signs of need.
Thanks for your reply. It's very helpful since I am new to aquarium keeping. A friend gave it to us when he had to move abroad.
BTW, I am inspired by your signature quote. I fully agree that our threat is within. Isn't it also true individually?
WOW!
The cloudiness is due to lack of flow/filtration thru your filter, by now it is minimal.
Accumulated debris and bacteria are fouling the tank.
And the old carbon is leaching organic contaminants back into the water.
Filters need to cleaned/maintained pretty much at least monthly, if not more often depending on stocking/feeding.
This will avoid your current problem(s) and others.
You also need to doing (if you aren't already) weekly water testing for pH, Ammonia (NH3), Nitrite (NO2) and Nitrate (NO3) and PWC's and gravel vacuuming. If you haven't been, I bet your NO3 is off the charts.
Do you have water test kits? Need good liquid test kits, API's are some of the best.
OK, time to clean and perhaps replace heavily fouled medias.
And the carbon is trash, trash it, no need to use it in a healthy aquarium.
Close inlet, close outlet, unplug, remove hoses, carry whole canister to tub, sink.
First try cleaning the pads, bucket of tap/dechlor'd water, go to town on the pads, don't be gentle, scrunch'em up, massage, knead, dunk and repeat with vigor.
If they are too fouled to come clean, going to have to replace.
Don't toss'em though, get'em as clean as you can, and put them on top of new padding. Trash'em in two weeks to a month, and add new padding or bio media.
Like I said, I double layer padding.
Cut new padding to fit tray, cut a X to poke the pipe thru, place old atop new, this keeps your beneficial bacteria healthy and maintains the nitrogen cycle.
Do you know about the Nitrogen Cycle?