Open it up over a bucket, media first
Switch the filter off and close the hose taps before disconnecting anything — a canister holds a surprising volume of water, and the whole job belongs over a bucket or a shallow tray with towels down. Lift the media trays out in order and set them aside in the sequence they came out, because the stack is a treatment line: coarse foam first to catch solids, biological media in the middle where cleaned water flows past, fine pad last to polish. Keeping that order matters, since biological media placed ahead of the mechanical stage clogs with the very debris the foams exist to intercept. Pour the canister's own water into your bucket as the rinsing supply — it is tank water, at tank temperature, with no chlorine, which is exactly what the bacteria need.
Rinse in tank water, replace almost nothing
Squeeze the coarse foams in the bucket until they release most of their load; they should come out cleaner, not sterile, and a faint discolouration worked deep into old foam is normal. Swish baskets of ceramic or sintered media in the same water just enough to shake off loose mulm — scrubbing them bright would scour off the biofilm you are trying to preserve. The one consumable is the fine polishing pad, which clogs beyond rinsing and can be replaced outright. If biological media ever genuinely needs replacing because it is crumbling, swap only part of it and leave the rest in service for some weeks so the colony reseeds the new material; replacing every tray in one session is how a routine clean becomes a cycle crash.
Impeller, hoses, and the seal that matters
While the head unit is off, pull the impeller and clear the grit and hair algae from its well — a gritty impeller is the usual source of a canister that has grown noisy or lost flow. Run a long flexible brush through the hoses, which slowly narrow with biofilm and algae, especially on the sunlit side of the cabinet. Examine the large O-ring around the head: it should be supple and evenly seated, cleaned of grit and given the lightest smear of the manufacturer's recommended lubricant if it looks dry. Most canister leaks are born at this seal during reassembly, from a ring pinched, twisted, or seated over a grain of sand, so the minute spent here is the cheapest insurance in the whole job.
Prime, leak-check, and watch the week after
Refill the canister with dechlorinated water or clean tank water before closing it, open the taps in the order the design intends, and prime until the hoses run free of air — a filter restarted half full of air will rattle, strain, and move little water. Watch the joints and the head seal for the first hour with a dry hand and a torch; a slow weep found now is a drip tray, while the same weep found tomorrow is a wet cabinet. Then treat the tank as probationary for a few days: glance at flow daily, test ammonia once or twice, and feed normally but not generously until the readings confirm the colony shrugged the service off.
How often is often enough
A canister on a moderately stocked tank typically needs opening every month or two, judged by falling flow rather than by the calendar alone — fine pads clog and impellers gum up long before the biological media needs attention. Waiting until flow collapses means the media has been marinating in trapped waste and the rinse becomes a rescue. Logging each service, what was replaced, and the readings afterwards as a scheduled duty in KinsLe's Care Teams, with the completed task timestamped, builds the service history that tells you this filter's real rhythm instead of a guess.