Most whole-home filter systems use standard Big Blue (20″ × 4.5″) or standard (10″ × 2.5″) housings. Both are designed for straightforward cartridge swaps without any plumbing work. The process is the same regardless of whether you're replacing a sediment filter, carbon block, or composite media cartridge.
This guide covers systems with bypass valves or mains shut-offs accessible to the homeowner. If your system is installed without an accessible shut-off, or is directly plumbed with no bypass, call your installer before attempting this. Proprietary housings (AquaCo Aragon, some Everpure systems) use different release mechanisms — check your manual.
- →Sediment: 3–6 months · Carbon block: 6–12 months · KDF/TAC: 2–5 years · UV lamp: annually. Stick to the schedule — don't wait for performance to drop.
- ✓The job takes 15 minutes for most whole-home systems. No plumber needed — just shut off the bypass valve first.
- →Tools needed: filter housing wrench, bucket, and replacement cartridges. Always shut off the bypass valve before removing any housing.
- ✗Overdue cartridges don't just stop filtering — they can harbour bacteria. A blocked sediment stage puts pressure on downstream stages.
- ✓Write the cartridge model numbers on a sticker inside the housing. Don't rely on memory or the supplier to have the right ones in stock.
How often to change each cartridge type
The single most common mistake is replacing all cartridges on the same schedule when they actually have different service lives. The sediment stage typically needs replacing more frequently than the carbon stage — especially in high-iron or high-turbidity water.
| Cartridge type | Typical life | Replace earlier if | Never exceed |
|---|---|---|---|
| Sediment (PP spun) | 3–6 months | Visible discolouration, flow drops | 12 months |
| Carbon block | 6–12 months | Chlorine taste returns, odour noticed | 12 months |
| GAC (granular activated carbon) | 6–12 months | Taste or odour returns | 12 months |
| Composite / Aragon | 6–12 months | Reduced flow, taste change | 12 months |
| KDF media | 2–5 years | Metallic taste returns | 5 years |
| TAC media | 3–5 years | Scale reappears on surfaces | 5 years |
| UV lamp | 12 months | Never — always annual regardless of appearance | 12 months |
| RO membrane | 2–5 years | TDS reading rises significantly | 5 years |
Carbon cartridges fail silently — they don't discolour or visibly clog. Once the adsorption capacity is exhausted, they stop removing chlorine with no warning. Replace on schedule regardless of appearance. A TDS meter or chlorine test strip can confirm performance if you're unsure.
What you'll need
The housing wrench is the only tool most people don't have readily available. They come in two sizes — one for 10″ housings, one for 20″ Big Blue. If you've misplaced yours, they're available from hardware stores and filter suppliers for under $10. Do not attempt to open a housing with a pipe wrench or pliers — you'll damage the housing.
Step-by-step: replacing the cartridge
Turn off the water supply
Use the dedicated filter shut-off valve if installed, or turn off your mains. If your system has a bypass valve, rotate it to bypass — this maintains supply to the house while the filter is offline.
Open a downstream tap (kitchen or laundry) to release line pressure. You'll hear a brief hiss as pressure drops. Leave this tap open while you work.
Release housing pressure using the relief button
Most Big Blue housings have a small red or black pressure relief button on top. Press this before attempting to unscrew — it vents residual pressure that can otherwise make the housing very difficult or impossible to open by hand. Hold a cloth over it as you press; a small amount of water will spray out.
If your housing has no relief button, the pressure should already be released from Step 1 — but allow 30 seconds after opening the downstream tap before proceeding.
Remove the housing bowl
Fit the housing wrench around the lower bowl and turn anti-clockwise (as viewed from below). The first quarter-turn is usually the hardest — Big Blue housings are designed to seal tightly under water pressure. Once broken loose, unscrew by hand.
Have your bucket ready — the housing holds 1–2 litres of water which will pour out as you lower it. This is normal.
Remove and dispose of the old cartridge
Lift the old cartridge straight out of the bowl. Sediment cartridges will be visibly discoloured — the colour tells you something about your water. Brown/orange: iron. Grey: general sediment and silt. Very dark: carbon dust or organic matter.
Note the cartridge size and part number before discarding — you'll need this for reordering.
Clean the housing bowl and inspect the O-ring
Rinse the bowl with clean water. For a thorough sanitise (recommended every second or third change), add a quarter-teaspoon of unscented household bleach to 500ml of water, rinse the interior, and flush with clean water before reassembling.
Locate the O-ring in the groove at the top of the bowl or on the housing head. Remove it, clean it, and inspect for cracks or flattening. A damaged O-ring causes leaks. Replacement O-rings are available from your filter supplier for $1–$3 — always keep a spare.
Apply a thin smear of food-grade silicone lubricant to the O-ring before refitting. Do not use petroleum-based lubricants — they degrade rubber O-rings.
Install the new cartridge
Unwrap the new cartridge and note orientation — most cartridges are not directional, but some (particularly carbon blocks with end caps) have a specific up/down orientation. Check the packaging.
Drop the cartridge into the housing bowl so it seats into the centre post. For Big Blue housings, there is no centre post — the cartridge sits freely in the bowl and self-aligns when the housing is reassembled.
Reassemble and hand-tighten only
Screw the bowl back onto the housing head clockwise. Hand-tighten firmly — do not use the housing wrench to tighten. The water pressure when you restore supply will finish the seal. Overtightening damages the housing threads and makes future removal very difficult.
Restore water supply slowly and check for leaks
Turn the water supply back on slowly rather than all at once — this allows the housing to pressurise gradually and seats the O-ring properly. Watch the housing junction for drips for the first 30 seconds.
A slow drip at the bowl join means the O-ring is not seated correctly. Turn off, disassemble, recheck the O-ring groove, re-lubricate, and reassemble.
Flush the new cartridge
Open a downstream tap and run water for 2–5 minutes. New cartridges — especially carbon blocks — release small amounts of harmless fine carbon dust on first use. The water may appear grey initially; this clears quickly. Do not drink this first flush.
Mark the change date on the housing or in a calendar reminder. Most people find a note written directly on the cartridge with a marker is the most reliable reminder system.
Troubleshooting common problems
Housing won't open
If the pressure relief button hasn't been pressed, residual line pressure can make the housing essentially impossible to open by hand. Press the relief button first, allow pressure to fully vent, then try again. If it's still stuck, check that the shut-off valve is fully closed — a partially closed valve can maintain enough pressure to resist opening.
Leaking after reassembly
Almost always an O-ring issue. The three causes: O-ring has a crack or flat spot (replace it), O-ring isn't seated properly in its groove (remove and reseat), or O-ring wasn't lubricated (apply silicone grease and reseat). A small amount of moisture on the outside of the housing that dries within an hour after pressurising is often just residual water from the bowl — not an active leak.
Low pressure after cartridge change
A new cartridge — especially a tighter-rated sediment filter or a carbon block — can cause a noticeable flow reduction compared to an exhausted cartridge. This is normal and is actually what filtration looks like. If the pressure reduction seems excessive, check that you've installed the correct cartridge format for your housing (10″ vs 20″, correct diameter).
I don't know what cartridge my system uses
The cartridge will have a part number printed on it. Note this before discarding. If it's illegible, measure the length and outer diameter — 10″ × 2.5″ and 20″ × 4.5″ are the two universal sizes. For proprietary formats (Aragon, Everpure, Puretec branded cartridges), contact the supplier directly. FilterOut's supplier directory includes contact numbers for all major Australian filter suppliers.
If your system uses proprietary Aragon or Disruptor® media (AquaCo systems), these must be sourced through AquaCo directly — generic Big Blue cartridges can be fitted in the housing but won't replicate the certified performance of the original media. For standard Big Blue housings, any brand's cartridge of the correct size and micron rating will work.