Ceramic water filters: how the candle works, which replacement to buy (Doulton, Southern Cross, Stefani), and when to scrub it

A ceramic water filter is the oldest filter still sold: a hollow candle of fired diatomaceous earth, hung in the top chamber of a gravity purifier, with pores too small for sediment, cysts and most bacteria and a core of carbon for the chlorine taste. The body lasts for decades; the candle is the filter, and it’s the part you buy again. For a Doulton, British Berkefeld or Southern Cross purifier, buy the Doulton Ultra Sterasyl ($99.95 at Southern Cross Pottery on 1 November 2026, also on Amazon Australia), the one candle here with a stated litre life. For fluoride, the Southern Cross Fluoride Plus ($96.45). For a Stefani purifier, the Aqua Elite ($36.90 at Bunnings). We can’t show Amazon prices; the Amazon buttons show today’s.

How a ceramic candle filters, and what it doesn’t

Doulton’s own description is the plainest: the ceramic is “a fine 3D sieve with a convoluted path through the wall”, so particles larger than the pores are trapped on the outside, and the activated carbon core “helps to improve the taste and odour of your water” by absorbing chlorine, with some reduction of pesticides, pharmaceuticals and heavy metals. Southern Cross quotes 0.2 micron absolute for its Doulton-made ceramic, which is the figure that puts cysts and bacteria on the outside of the wall. The makers add silver to the ceramic (Doulton’s BioTect, Stefani’s colloidal silver) to stop bacteria growing on the candle itself.

What a plain ceramic candle doesn’t do: viruses, which are smaller than the pores and which no candle here claims; dissolved salts; and fluoride, unless the candle carries fluoride media. Southern Cross prints “does not remove fluoride” against the Ultra Sterasyl and “does not remove PFAS” against the Fluoride Plus, which is the kind of honesty we wish every listing managed. Speed is the other limit. Gravity pushes water through a candle at about 900 mL an hour by Southern Cross’s figure, so a 10 L purifier fills overnight, not over lunch.

Which replacement candle should you buy?

Buy by the purifier first and the job second. For Doulton, British Berkefeld and Southern Cross bodies, and most others with a wingnut mount, the Doulton Ultra Sterasyl is the all-rounder: ceramic outer, granular carbon and a heavy-metal media, with the listing claiming over 99% of PFAS (up to 99.38% of PFOA and PFOS), sediment, microplastics, E. coli and trace organics, replaced “every 1500 litres or every 6 to 9 months, whichever comes first”. It doesn’t touch fluoride. If fluoride is why you bought a gravity filter, the Southern Cross Fluoride Plus claims 97% and is made for SCP by Doulton’s ceramic works in England, 0.2 micron absolute on the Amazon listing, and the SCP MAX claims 92% fluoride and 95% PFAS in one candle for $102.75. Doulton’s own Ultra Fluoride candle claims 99% up to 1,950 ppm and six months; Amazon had one left when we checked.

For a Stefani ceramic purifier (10 L, 15 L, terracotta or stainless), Stefani sells three candles at Bunnings with the same ceramic shell and silver: the Aqua Balance ($27.40) for chlorine, taste and sediment, the Aqua Endura ($32.50) with a carbon block core sold as longer-lasting, and the Aqua Elite ($36.90) adding lead, heavy metal and PFAS claims. None of the three listings gives a micron rating, a litre life or a percentage, so the Elite’s extra $4.40 buys claims rather than numbers; it’s still the one we’d fit. The multi-stage “8-stage” benchtop purifiers sold online take a dome, not a candle: the Orku ceramic dome at Bunnings is 0.2 to 0.5 micron, 99 mm across, with no reduction claims at all on its listing.

Cleaning the candle, and when it’s finished

The brown film that builds on the outside is the filter working, and it’s why flow slows. Lift the candle out, scrub the ceramic under running water with a soft brush or a plastic scouring pad until it’s pale again, rinse and refit; Doulton says its filters “can be cleaned between changes” and keeps a video for it. Never use detergent, and never scrub the carbon end or the thread. On tank water expect to do it every two to four weeks; on town water a couple of times a season.

Cleaning restores the ceramic; nothing restores the carbon. That’s why the interval is set in months and litres rather than by flow: Doulton says “we recommend changing the ceramic water filters from Doulton every 6 months”, the Ultra Sterasyl listing says 1,500 L or six to nine months, Southern Cross says up to a year with six months recommended. Write the fit date on the candle with a marker. A candle that has been scrubbed thin, cracked, or left to dry out for weeks should be replaced regardless of date, because a crack in the wall is a hole in the sieve.

Ceramic on tank water

Southern Cross names tank and bore water as uses for its candles, and a ceramic candle is the right kitchen step for a tank household: it takes out the silt and, by the makers’ claims, cysts and bacteria. It is not the household’s disinfection. enHealth’s rainwater guidance says that if in doubt about the microbiological quality of tank water it should be disinfected or boiled, and no candle here claims viruses. Read the rainwater tank filter guide for the filter-then-UV setup on the house line, and treat the gravity purifier as the polish on top.

The one trap

Buying the candle by price and getting the wrong chemistry. A $27.40 Stefani Balance and a $99.95 Doulton Ultra Sterasyl are both “ceramic candles”, and so is a $96.45 Fluoride Plus, and they do three different jobs: taste, PFAS and heavy metals, fluoride. Decide what you want out of the water, then check the listing says it in a number, then check the thread fits. The fluoride guide covers why reverse osmosis beats any candle if fluoride removal has to be reliable rather than 92 to 99% by the maker’s test.

What we left out and why

• British Berkefeld 7 inch Ultra Sterasyl 4-pack, Doulton UltraCarb and Doulton Ultra Sterasyl from other Amazon sellers. The same Doulton candles in other packs or sizes; the single Ultra Sterasyl above is the one Southern Cross sells for Australian purifiers.
• Generic “ceramic activated carbon candles” 2-packs (Amazon Australia). No micron rating, no life, no maker.
• Provecta and 4-pack ceramic domes (Amazon Australia). Domes for the multi-stage benchtop units; the Orku at Bunnings is the one with an Australian returns desk.
• Gravity fluoride removal cartridges from unnamed sellers (Amazon Australia). No featured offer when we checked.
• Stefani 10 L, 15 L, terracotta and stainless purifiers. The bodies, covered in the benchtop guide.
• Berkey Black Berkey elements. Not ceramic, and Berkey isn’t distributed in Australia; the benchtop guide explains.