Pool-chemical safety: Follow the product label. The CDC pool-chemical guidance says to keep each chemical in its original labeled container, store chemicals separately in a dry, well-ventilated area, and never mix chlorine with acids or different chlorine products.
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The Pentair Rainbow 320 is a good inline feeder when the return plumbing has the space, orientation, and service access required by the manual. It keeps tablets contained at the equipment pad and gives you an adjustable flow path. Skip it if cutting the return line is impractical, an off-line retrofit is easier, or routine trichlor use no longer fits the pool’s stabilizer level.
Verdict
Buy it for: a permanent residential pool with compatible plumbing, a planned inline installation, and an owner who already intends to use label-approved trichlor tablets.
Skip it for: temporary or seasonal soft-sided pools, equipment pads with poor access, pools that need an off-line bypass feeder, or water that already has excessive cyanuric acid.
The Rainbow 320 controls water movement through a tablet chamber. It does not sense chlorine demand, measure water chemistry, or decide how many tablets the pool needs.
What to verify before buying
Plumbing position
An inline feeder becomes part of the return line. Confirm pipe size, straight-run space, flow direction, clearances, and the position relative to the heater and other equipment from the current Pentair installation manual. Use a qualified installer when plumbing or local code is outside your experience.
Tablet chemistry
Do not treat “chlorine tablet” as a universal format. Use only chemistry and sizes explicitly permitted by the feeder manual and sanitizer label. Never add a different chlorine type over residue from another product. If the feeder history is unknown, stop and get manufacturer or professional guidance before loading it.
Service access
The lid and control must remain reachable after installation. Leave room to depressurize, open, inspect, and service the feeder without leaning over electrical equipment or hot plumbing. A feeder that technically fits but cannot be serviced safely is the wrong installation.
How it compares
| Feeder | Best use | Main trade-off |
|---|---|---|
| Pentair Rainbow 320 inline | Permanent return line with planned installation | Requires cutting and correctly arranging plumbing |
| Hayward CL220 off-line | Retrofit where a bypass tube is easier | Adds tubing and connection points to inspect |
| Floating dispenser | Small pool or no-plumbing setup | Moves in the pool and can rest against surfaces |
The Rainbow 320 is the cleanest-looking solution of the three when the equipment pad is already being built or replumbed. The CL220 is often easier when the main return line should remain intact. A floater is cheaper, but it gives up equipment-pad containment and precise placement.
Trichlor trade-offs
Trichlor is slow-dissolving and stabilized. It can supply chlorine steadily, but routine use also contributes cyanuric acid and tends to affect pH. Test free chlorine, pH, and stabilizer as the product label and pool conditions require. Turning the feeder higher is not a substitute for diagnosing low chlorine, poor circulation, or an overloaded filter.
If cyanuric acid is already high, liquid chlorine or a salt chlorine generator may make more sense because those routes do not keep adding stabilizer through trichlor tablets.
Ownership and maintenance
Follow the manual’s shutdown and depressurization procedure before opening the lid. Inspect seals, fittings, the control, and the body on the stated schedule. Replace damaged parts with specified components; do not improvise around a chemical feeder.
Keep unused tablets in their original container, separate from acids and every other pool chemical. Never use the feeder as storage, and never leave mixed or unidentified residue inside.
Final recommendation
Choose the Pentair Rainbow 320 when an inline installation genuinely matches the plumbing and trichlor still matches the water. Choose the Hayward CL220 when an off-line retrofit is more practical. Choose a floater only for a smaller, label-compatible pool where installed equipment is not justified.
See Also
If you are weighing this model, also compare it with Clorox XtraBlue 3-Inch Chlorine Tablets Review, Doheny's 10-Lb 3-Inch Chlorine Tablets Review, and Foamy Pool Water: Are Chlorine Tablets the Cause?.
For broader context before you decide, Best Chlorine Tablets Under $50: What to Buy and Saltwater Pool Chlorine Generator vs Tablet Feeder: Which Is Better for Pool Owners? help round out the trade-offs.