Diameter alone is not chemical or installation approval; check the documented example in the Rainbow 320 exact-model installation approvals .
A tablet fits a feeder only when the exact feeder manual approves its chemistry and format. Diameter is one part of compatibility. Start with the equipment label and the chemical’s original container, not a caliper or a trial insertion.
Build a compatibility record for the installed feeder
| Field | Evidence to collect without opening or handling chemicals unnecessarily |
|---|---|
| Feeder identity | Manufacturer, complete model suffix and manual revision |
| Sanitizer identity | Active ingredient and product name from its original label |
| Permitted form | Tablet, stick or other form explicitly approved by the feeder manual |
| Nominal diameter | Manufacturer’s stated tablet size, compared with the feeder manual |
| Feed route | Whether the sanitizer label permits this particular type of feeder |
| Previous contents | Known product history; unknown residue is an unresolved compatibility issue |
Mark each field confirmed, conflicting, or unknown. A physical match cannot overrule a conflict elsewhere in the record. If the previous chemical is unknown, do not top up, mix products or improvise a cleaning procedure. Ask the feeder and chemical manufacturers how to proceed.
Why a family name is insufficient
The Hayward CL200/CL220 manual specifies slow-dissolving trichlor tablets or sticks and excludes other chemical types. The Pentair Rainbow 320 manual describes its own approved tablet formats and chemical restrictions. Permission in one manual does not transfer to another feeder.
Even where a manual lists more than one permitted sanitizer, that does not permit mixing them or changing over a feeder containing residue. Keep the original product identity attached to the equipment’s maintenance record. Follow the exact manufacturer’s procedure for servicing, including isolation, pressure and protective equipment requirements.
What to do when an apparently correct tablet will not fit
Stop. Do not cut, crush, shave or force the tablet; do not enlarge a feeder opening. Recheck the complete feeder model and the product’s labeled nominal size. Contact the manufacturer with those identifiers and photographs of the external labels. There is no need to place measuring tools against a tablet to make that enquiry.
A seller’s “universal” claim is weaker evidence than the instructions for the actual chemical and feeder. If the manufacturer cannot confirm compatibility, choose a product explicitly approved for the equipment rather than experimenting with the opening.
Keep a useful replacement record
Save the approved product name, active ingredient, tablet size and applicable manual together; if the question is which tablet to buy rather than whether one fits, start with choosing chlorine tablets from the label and equipment . When buying a replacement, compare all four fields; matching the old package color or the word “chlorine” is insufficient. Record a product change before it reaches the equipment pad so another household member does not unknowingly refill over it.
If you are replacing the feeder itself, the model and plumbing fit map covers purchase-time installation differences. This guide resolves compatibility for equipment already identified; it does not prescribe a dose or an installation design.
The record above is an editorial decision aid based on the linked manuals and CDC chemical-separation guidance , checked September 23, 2026. It is not a physical fit test of every tablet brand.