Pentair Rainbow 320 and 300

Pentair sells two feeders for home pools: the inline 320, glued into the return line, and the freestanding offline 300, fed through two small tubes. The 300 also comes as the 302 spa feeder and in two taller versions, the 300-19 and 300-29, and as the commercial 300-29X. The Rainbow name survives in Pentair's manual links, on its silicone lubricant and in one of its check valve names, while the manuals themselves call the feeder Lifegard in places. How tablet chlorinators work covers where any feeder goes and what never goes in one. This page is about Pentair's: what its ratings mean, how its refill differs from Hayward's, and the parts.

What the gallon ratings mean

Pentair's product page says the 320 treats 6,500 to 27,000 gallons. The catalog's sizing chart shows how that range is built. It's how many gallons the feeder can raise by a given amount in a day:

• At 10 ppm a day: 6,700 gallons on the 320, 11,900 on the 300
• At 5 ppm a day: 13,400 on the 320, 23,800 on the 300
• At 2.5 ppm a day: 26,800 on the 320, 47,600 on the 300

Two assumptions sit under every figure, and the chart's footnote gives both. They're based on 1-inch trichlor tablets, and 3-inch tablets, sticks or bromine lower the results. And they assume 24 hours of circulation. For an 8-hour turnover, the chart says to divide by 3.

Put together, a 320 on 3-inch tablets and an 8-hour pump day covers well under a third of what the headline number suggests. The commercial 300-29X manual puts the tablet difference at less than 40% for 3-inch tablets against 1-inch.

The 320 has one more setting. Bottom feed, the way it ships, is rated at 0.67 pounds a day. Top feed, a conversion using the plugged opening above the valve and an extra length of tubing, is rated at 1.75. Pentair's order of fixes for a 320 that can't keep up is 1-inch tablets first, then top feed, and it warns that top feed can over-chlorinate in normal conditions.

Setting the dial

Higher numbers feed more. Pentair's example is 2 in winter and 3 in summer, and its instructions are to test daily for the first five days and to make small, gradual changes. When heat, sun or a busy weekend is coming, it suggests raising the feed a day or two ahead.

Before starting the feeder, Pentair wants the water balanced and holding 1.0 to 1.5 ppm of chlorine, or 2.0 to 4.0 ppm of bromine.

Refilling with the pump running

This is where Pentair's feeders differ from Hayward's. The 300 and 320 recharge steps are:

1. Close the control valve and stop the pump.
2. Wait a minute for the water and fumes to drain out of the feeder.
3. Turn the pump back on with the valve still closed. The built-in check valve keeps water out.
4. Take off the cap, fill with the right size tablets, and put the cap back with a clean, lubricated O-ring, hand tight.
5. Open the valve back to its setting, and check the tubing while you're there.

That only works on a feeder above the water level. Mounted below it, Pentair says a drain valve must be fitted, and the feeder drained into a container before the cap comes off, or it splashes strongly chlorinated water back at you. The 300-29X's recharge is different again: pump off and the valve set to 5, then the cap comes off.

What goes in it

Only clean, slow-dissolving trichlor or bromine tablets, and never a mix. Every Pentair feeder manual says calcium hypochlorite is not to be used in any form, and that mixing it with trichlor or bromine can cause a fire or explosion. They add three rules owners miss:

• Shock. Turn the feeder off or take the tablets out until the shock has fully dissolved. Granules getting into the feeder are the danger; shock already dissolved in the water is safe with the tablets.
• Dirty tablets. Keep dirt and debris out of the feeder at all times.
• A feeder that came with the house. If you don't know what was in it, flush it thoroughly with fresh water before loading it.

The 320 takes 1-inch or 3-inch tablets, and the optional spa chamber takes 1-inch ones for a spa or hot tub.

Where it goes

After the heater, the pool cleaner and any valves, and never before the heater, which highly chlorinated water can damage. With no heater, after the filter. Never in copper plumbing. And with a heater on the system, Pentair's feeder manuals say a fireman's switch must be installed, to protect the check valve and anything else heat can harm.

For the 320, Pentair wants at least 6 inches of straight pipe between an elbow and the feeder's inlet, because an elbow right at the inlet makes turbulence that stops water being scooped in. If any equipment on a 2-inch system has smaller fittings, the 1½-inch bushings go into the feeder's inlet to build pressure.

For the 300, the outlet line goes after the heater. With a heater, the manual puts the inlet between the filter and the heater, and without one, between the pump and the filter. The check valve sheet adds that the pump and filter position gives more flow.

Extensions

A 10-inch extension, R172087, roughly doubles a 300 or 320's capacity and time between refills, and the 20-inch R172283 roughly triples it. The bigger chamber also feeds more at the same setting, so Pentair says to watch the readings for several days afterward and readjust. On a freestanding 300, secure the base so the taller feeder can't tip over. The extensions aren't for the 300-19 or 300-29, which already have the taller chamber, and the 2025-2026 catalog lists the 10-inch only.