A missing model number does not prevent you from buying a Siliphos refill. In most cases the housing can be identified by its physical dimensions, connection thread, and end-cap design, and the correct refill is then matched on cartridge size, media form, and the housing’s intended duty. The real risk is not “no model number” — it is ordering a refill that fits the shell but contains the wrong media, or trying to refill a housing that was designed as a sealed, disposable unit.

Why the model number matters less than the measurements

Housings used for scale-inhibiting polyphosphate media are rarely proprietary to one brand. Many are standard filter housings — slimline or “Big Blue” style bodies, in-line cartridges, or refillable tubes — sold under dozens of labels. The label on the bracket or cap is often a private brand, while the actual housing and thread follow a common industry pattern.

What a supplier actually needs to match a refill is geometry and duty, not a catalogue number. Two things must match:

• Mechanical fit — the refill has to sit in the sump, seal correctly, and connect to the head without leaking.
• Functional fit — the media has to be the right type, in the right quantity, and used within the flow and temperature conditions it was designed for.

Step 1: Confirm the housing is actually refillable

Before measuring anything, check whether the housing takes a replaceable insert or is a sealed disposable cartridge.

• Refillable type: a reusable tube, cage, or porous sleeve that opens, unscrews, or splits so media can be poured in and the cap reseated. These are the housings where buying loose Siliphos crystal or a pre-measured refill bag makes sense.
• Sealed cartridge type: a welded or crimped cartridge with no serviceable opening. These cannot be refilled — you replace the whole cartridge, and the correct part is identified by size and media description, not by refilling.
• Loose-media sump type: some installations use a plain housing sump partly filled with crystal and topped with a screen or pad. These are refillable, but the media volume must be controlled so the housing still seals and the flow path is not blocked.

If the cartridge is sealed and the original part number has worn off, the practical solution is to measure it and buy an equivalent cartridge — not to force a refill into a housing that was never designed to be opened.

Step 2: Measure these six things

Use a ruler or caliper and write the figures down in millimetres. Do not rely on nominal descriptions such as “10-inch” alone, because nominal labels refer to the housing, not always to the exact cartridge length.

Where to look for a hidden model number

Even when nothing is visible from outside, identifiers are often present:

• Inside the head or cap, around the sealing face.
• On the underside or base of the sump, which is rarely cleaned.
• On the mounting bracket, behind the housing body.
• On the original installation invoice, commissioning sheet, or maintenance log.
• On the shut-off valve or bypass assembly, which may carry the same brand as the housing.

A photograph of the open housing next to a ruler is often more useful to a supplier than a partial or unreadable part number.

Step 3: Match the media, not just the shell

A refill that fits physically can still be functionally wrong. These terms are frequently used interchangeably in the market, but they do not describe the same job:

• Scale inhibition — slowing or preventing the formation of new mineral scale, typically by keeping hardness minerals in a dispersed or non-crystalline form. This is the usual purpose of polyphosphate-based media.
• Water softening — removing hardness ions through ion exchange with resin and adding sodium or potassium to the water. Polyphosphate media do not do this.
• Scale removal — dissolving or physically breaking down existing deposits already formed in pipes or equipment. A polyphosphate refill is generally not a scale remover.
• Filtration — trapping suspended particles. Some housings combine sediment filtration with polyphosphate media; the two functions are separate.
• Corrosion inhibition — some phosphate treatments form a protective film on metal surfaces, but this is a distinct function and depends on the specific chemistry, dose, and water conditions.
• Disinfection — killing or inactivating microorganisms. No polyphosphate refill performs this function.

“Siliphos” is a trade name that has become widely used as a generic term for slow-dissolving polyphosphate crystal media. Products sold under this description are not necessarily chemically identical, and dissolution rate, particle size, and suitable operating conditions can differ between suppliers. If your system was commissioned with a specific product, confirm the replacement is compatible rather than assuming equivalence from the name alone.

Step 4: Check the operating conditions before ordering

Two identical housings can need different refill quantities or replacement intervals because of the water and the flow. Provide the following where known:

• Purpose of the installation — protecting a boiler feed line, a coffee machine, a reverse osmosis pre-treatment stage, a plate heat exchanger, or domestic plumbing.
• Water hardness, and whether it varies seasonally or by source.
• pH and temperature range.
• Peak and continuous flow rate through the housing.
• Whether chlorine or other oxidants are present.
• Any pre-treatment already installed upstream.

Contact time between water and polyphosphate media falls as flow rate rises, and dissolution behaviour changes with temperature. This is why a supplier cannot responsibly quote a universal service life. Replacement intervals must be set from the actual product’s documented guidance and confirmed against your site conditions — by measuring residual phosphate, by inspection of the media charge, or by the schedule recommended for the specific product.

Step 5: Decide between a refill and a replacement

Use this quick logic:

1. The housing opens and takes a replaceable insert → a refill is viable if you can match media type and quantity.
2. The cartridge is sealed → buy a replacement cartridge matched on dimensions and media description.
3. The housing is cracked, the thread is worn, or the head seal is damaged → replace the housing; a new refill will not fix a leaking body.
4. The housing brand is unknown and no refill matches all dimensions → replace the complete housing with a documented model so future refills are straightforward.

Do not assume food-grade means drinking-water approved

Media marketed as food grade is not automatically approved for potable water use. Drinking-water suitability depends on the exact product, the dose, the installation, and the regulations of the destination market. If the treated water is intended for human consumption, request the relevant documentation for that specific product and confirm it against local requirements before installation.

FAQs

Can I use loose polyphosphate crystal to refill any housing?

No. The housing must be designed to be opened and resealed, and the fill volume must allow the head to close and the water to pass through the media rather than around it. Sealed cartridges should be replaced, not cut open.

How do I know how much media to use?

Start from the original charge weight or fill level, then confirm with the supplier against your flow rate and water conditions. Underfilling can cause bypass; overfilling can block flow or prevent the housing from sealing.

Will a polyphosphate refill soften my water?

No. It inhibits scale formation but does not remove hardness ions. If you need softened water, you need an ion exchange softener or another appropriate process.

What if the measurements match two different refills?

Then the sealing style or media form decides it. Send photographs of the open housing, the old insert, and the head seal with your measurements. That usually settles the match.

Information to send with a refill inquiry

If you are sourcing a Siliphos or polyphosphate refill for an unlabelled housing, include the following and you will get a usable answer rather than a guess: the six measurements listed above, photographs with a ruler in frame, whether the housing is refillable or sealed, the application and equipment being protected, water hardness, pH and temperature if available, continuous and peak flow rate, the quantity required, and the destination market if drinking-water compliance is relevant. ENVO CHEMICAL can review those details against the available polyphosphate media options and advise on the closest match — but only the measurements and water data you supply will determine whether the refill is genuinely suitable.