Pool-chemical safety: Follow the exact feeder manual and sanitizer label. The CDC pool-chemical guidance says to keep chemicals dry, separate, and in original manufacturer-labeled containers. Never mix chlorine products, and never add water to a chemical container.
Tablet diameter is an equipment-fit and erosion variable, not a dose setting. A 1-inch tablet is not automatically gentler, and a 3-inch tablet is not automatically stronger or longer lasting in every feeder. Choose the format that both the feeder manual and the chemical label permit, then use water tests to establish the setting.
Compare the device purchase separately from the refill purchase
If your approved feeder already accepts the current tablet format and the water result is controlled, a cheaper bucket in a different diameter is not automatically a saving. It may require a different dispenser, a revised permitted setup and closer follow-up after the change.
Put the two possible orders side by side: the existing approved refill product, and the proposed refill plus any correctly matched device. Include package quantity, active ingredient, labeled available chlorine and delivery price. Do not compare tablet counts as if each piece supplied the same amount.
The Poolmaster examples illustrate the hardware boundary: model 32155 is the larger-tablet option and 32157 is the small-tablet option. A similar floating body does not make their permitted formats interchangeable. For a Rainbow 320 that permits both, follow its specific procedure rather than replacing hardware solely because the diameter changes.
This is a purchasing comparison, not a recommendation to switch sizes. If the current chemistry no longer fits the water balance, changing from 3 inches to 1 inch within the same stabilized chemistry does not solve that problem.
Read the package before comparing sizes. A nominal diameter does not state tablet weight, the count in a bucket or available chlorine, so compare labeled net weight and stated contents. A package with twice as many tablets is not necessarily twice as much sanitizer, and equal weights still do not make application procedures interchangeable. Do not handle or weigh loose tablets to complete a shopping comparison. A feeder that accepts two sizes still has one set of instructions, so do not mix sizes or products to use up leftovers unless the manual expressly permits it. If the listing, the shipped container and the feeder manual disagree, or a seller claims “universal fit,” keep the product out of the feeder and contact the supplier or manufacturer with the original label and product identifier. For an installed feeder of uncertain identity or prior contents, start with the compatibility record .
The key correction: smaller is not a smaller dose
Smaller tablets can expose more total surface area for the same mass. In Pentair’s Rainbow 320 manual, the manufacturer says that if 3-inch tablets do not provide enough chlorine residual, switch to 1-inch tablets because the smaller format erodes faster.
That exact instruction disproves the common shortcut that 1-inch tablets always provide finer or weaker dosing. Erosion depends on feeder geometry, water contact, tablet surface area, formulation, pump schedule, flow, and temperature. Tablet count alone does not state chlorine output.
Exact dispenser examples
Poolmaster’s current catalog distinguishes two similar floaters:
| Model | Published tablet fit | Buyer action |
|---|---|---|
| Poolmaster 32155 | Up to 3-inch tablets or sticks | View exact product and confirm sanitizer label |
| Poolmaster 32157 | Up to 1-inch tablets or sticks | Search exact model and confirm sanitizer label |
| Pentair Rainbow 320 R171096 | Manufacturer permits 1-inch or 3-inch slow-dissolving trichlor for pools | Follow the exact installation and operating guide |
Physical fit is only the first gate. The chemical active ingredient, feeder compatibility, pool material, water balance, and label directions still control use.
What tablet size changes
Chamber fit
A 3-inch tablet will not fit every compact floater or spa chamber. A pile of 1-inch tablets can have a different water-contact pattern from a few 3-inch tablets. Do not break a tablet or leave a cap partly closed to force a format into the wrong chamber.
Erosion rate
In a feeder that permits both sizes, changing surface area can change erosion. Pentair’s Rainbow documentation also separates stored tablet count, stored mass, and maximum erosion. Those are different measurements and should not be collapsed into a universal refill interval.
Refill pattern
A larger individual tablet may remain physically present longer in some floaters, but actual refill timing depends on permitted load, exposed openings, circulation, water temperature, formulation, and target residual. Diameter alone cannot predict a refill date.
Handling
One 3-inch tablet can mean fewer individual pieces to handle for the same approximate mass. A container of 1-inch tablets may be easier to load into a narrow chamber. In both cases, use dry dedicated protection and tools as the label directs, and keep the original container closed between uses.
Chemistry matters more than diameter
Confirm the active ingredient. Many slow-dissolving pool tablets are trichlor, which adds chlorine and cyanuric acid and can affect pH. A 1-inch trichlor tablet and a 3-inch trichlor tablet share those chemistry trade-offs even though they erode differently.
Do not treat calcium hypochlorite, bromine, dichlor, or an unidentified tablet as another size of the same product. Different chlorine products can react dangerously when mixed directly or through contaminated equipment. Never load a new chemistry over residue.
How to change sizes safely
Only consider a switch when the exact feeder manual permits both sizes and the sanitizer label permits that feeder. Then:
- Read the feeder shutdown and refill procedure.
- Confirm the existing product identity and residue history.
- Do not change chemistry merely to change diameter.
- Follow the manual for loading and initial setting.
- Test free chlorine and pH at the directed interval after the change.
- Track cyanuric acid when using stabilized chlorine repeatedly.
- Stop adjusting and seek qualified advice if control becomes uncertain. Follow the manual for any shutdown or removal; do not handle wet tablets to improvise a reversal.
Do not copy a dial setting from another pool. Pump schedule, sunlight, temperature, bather load, circulation, pool volume, and water balance all affect the result.
Storage is the same safety problem for both
Keep tablets in the original manufacturer-labeled container, closed, dry, below the temperature limit on the label, out of direct sun, and separated from acids, fuels, metal tools, fertilizers, other chlorine products, children, and pets. A garage that also stores fuel or yard chemicals may be the wrong location.
Do not use an unmarked bin, food container, or feeder as long-term storage. Do not return damp, broken, or partly dissolved material to the original package.
Final recommendation
Use 3-inch tablets when the exact feeder and sanitizer label permit that format and the measured output can be controlled. Use 1-inch tablets when the exact equipment calls for them or, as Pentair documents for the Rainbow 320, when that permitted format is needed for greater erosion and residual.
Choose from the manual, chemistry, and water test. Do not choose 1-inch tablets for a presumed smaller dose or 3-inch tablets for a presumed universal value advantage.
For exact installed-feeder behavior, use the model and plumbing-fit map . For stabilized-chlorine trade-offs, compare trichlor tablets with dichlor granules .