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A Filter Maintenance Schedule You Will Actually Keep
Filters rarely fail because they were the wrong filter. They fail because the impeller was never inspected, the sponge was rinsed under the tap, or every piece of media was replaced on the same afternoon. Below is a routine built around what actually goes wrong, with the jobs spaced so they do not compound each other.
Weekly: two minutes, no tools
- Check the water level. Evaporation lowers the level until a hang-on-back intake starts drawing air. Topping up with dechlorinated water takes seconds and prevents an impeller running dry.
- Watch the outflow. You are looking for a change, not a number. A return that used to break the surface and now dribbles means the mechanical media is loading up.
- Look at the intake strainer. Leaves, snails and plant trimmings park there and choke flow long before the sponge does.
That is the whole weekly job, and it catches most problems while they are still trivial.
Every two to four weeks: the mechanical rinse
Do this during a water change, so you have a bucket of old tank water to hand.
- Siphon out your usual volume for the water change and set a bucket of it aside.
- Switch the filter off. Remove the coarse sponge and squeeze it out in that bucket until the water runs murky rather than black.
- Inspect the fine floss. If it stays grey after rinsing, replace it — floss is the one genuine consumable in the stack.
- Put everything back in the original order, coarse first, and restart.
Never rinse media under the tap. Chlorinated water kills the bacterial colony living on the sponge, which is exactly what you are trying to protect. This is the single most common way a stable tank is knocked back into cycling.
Every three to four weeks: chemical media
If you run activated carbon, this is its working life. Past four weeks it is not harming anything, but it has stopped adsorbing and is simply occupying space that could hold something useful.
Pull carbon out entirely during any medication course, because it will strip the treatment straight back out of the water, then put fresh carbon in afterwards to clear the residue. Refills for the units we sell are listed under filter media and cartridges.
Every three to six months: the deeper service
This is the canister interval, and the point at which a hang-on-back deserves more than a sponge squeeze.
- Impeller and shaft. Pull the impeller out, clean the magnet and the housing with a soft brush, and look at the shaft for grooving. A worn shaft is the usual cause of a filter that has become noticeably louder.
- Hoses and O-rings, on a canister. Check the seal for twists, nicks and dryness, and put a smear of silicone grease on it before reassembly. A dry O-ring is how canisters end up leaking on the cabinet floor.
- Housing. Biofilm builds up on the inside walls. A rinse in old tank water is enough.
The two jobs that must never share a week
Rinsing the mechanical media and disturbing the biological media are both mildly disruptive on their own and genuinely risky together. The same goes for a deep filter service combined with a large water change, a substrate vacuum and new fish.
The rule we give people at the counter: one disruptive job per week. Service the filter this weekend, do the heavy gravel vacuum next weekend, add the new fish the weekend after. Nothing here is urgent enough to justify stacking them.
What almost never needs doing
Biological media — ceramic rings, sintered glass, porous blocks — should be rinsed gently in old tank water only when visibly clogged, and otherwise left alone for years. If you do have to replace it, do a third at a time with a month between, so the new material is colonised from the old.
Complete media replacement is not maintenance, it is a reset. There is almost no scenario in normal fishkeeping where it is the right answer.
Keep a note
A line in a notebook or a phone reminder — date, what you did, anything you noticed — takes ten seconds and turns a vague worry into a fact. When water goes cloudy three months from now, the first useful question is what changed, and a maintenance log answers it immediately.
Signs it is time to replace rather than service
- Flow is still well down after a full clean and a new impeller.
- The housing is cracked, or the seal will not hold after a fresh O-ring.
- The tank has been restocked well past what the unit was sized for.
The first two are genuine end-of-life. The third is a sizing question, and there is a full guide to it elsewhere on this journal. Either way, every unit in our filtration range lists the tank volume it is rated for, and the FAQ covers the questions that come up most. If you would rather talk it through, get in touch.
From our shelves
Products in this store that relate to what is covered above:
Prices are in US dollars. Delivery timings are on our shipping policy page and the return and refund policy sets out the window if something is not right.
