Best Automatic Pool Chlorinators
The best automatic pool chlorinator for most in-ground pools is the Pentair Rainbow 320, an off-line tablet feeder that mounts beside your equipment pad and drips a steady, adjustable dose of chlorine into the return line. An automatic chlorinator (also called an erosion or tablet feeder) is a canister that holds a stack of 3-inch trichlor tablets and dissolves a little off them as pool water passes through, so you refill it every few weeks instead of tossing tabs in a floater by hand. It is not a salt system: a salt chlorine generator makes its own chlorine from dissolved salt, while a chlorinator just meters out the tablets you buy. The two decisions that actually matter are off-line versus in-line and getting the install right, because a feeder plumbed in the wrong spot will quietly eat your heater. Here are the picks, and what to know before you buy.
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Pentair Rainbow 320 Off-Line Chlorinator
Who it is for: Most in-ground pools that want a fill-and-adjust tablet feeder that is safe to plumb and easy to service.
- +Off-line design mounts next to the pad and taps the return line with two small tubes, so it sits outside full pipe flow and a leak will not drain the pool.
- +Holds up to about 9 pounds of 3-inch trichlor tabs, roughly a few weeks of feeding for an average pool, so refills are infrequent.
- +A simple dial meters the feed rate, and rebuild parts (o-rings, check valve, control valve) are cheap and stocked everywhere when they wear.
Watch out: Trichlor tabs add cyanuric acid with every dose, so track stabilizer with the cyanuric acid calculator, and never load cal-hypo or any other chemical into a feeder that has held trichlor.
Hayward CL200 In-Line Chlorine Feeder
Who it is for: New builds and re-plumbs where you want the feeder built into the return pipe as the last piece of equipment.
- +Plumbs directly into the return line, a compact and permanent install with no separate mounting bracket.
- +Threaded lid and a positive seal handle high tablet loads for larger pools.
- +Adjustable control knob dials the feed rate from a trickle up to heavy feeding for peak season.
Watch out: In-line feeders sit in full flow, so they must go after the filter and heater, and a working check valve is required so chlorine gas cannot migrate back to the heat exchanger when the pump is off.
Pentair Rainbow 171 In-Line Feeder
Who it is for: Spas, hot tubs, and small above-ground pools where a full-size feeder would overdose the water.
- +Small capacity meant for low water volumes, so it feeds a rate that a few thousand gallons can actually use.
- +Handles chlorine or bromine tabs, which makes it a common choice for spas that run bromine.
- +Compact in-line body fits the tight plumbing on a spa pack or a small above-ground system.
Watch out: Small water volumes swing fast, so confirm your real gallons with the pool volume calculator and start the dial low. For bromine versus chlorine in a spa, see bromine vs chlorine.
Hayward CL220 Off-Line Chlorine Feeder
Who it is for: Owners running a Hayward pad who want an off-line feeder that matches their existing pump and filter.
- +Off-line install like the Rainbow 320, so it stays out of full flow and is simple to isolate and service.
- +Large tablet capacity for in-ground pools, with a clear control dial for the feed rate.
- +Standard Hayward unions and parts make it a clean addition to an all-Hayward equipment pad.
Watch out: Off-line or in-line, the feeder is always the last stop before the water returns to the pool. Put it downstream of the heater, never before it.
What actually matters when buying
Off-line beats in-line for most retrofits. Off-line feeders mount beside the pad and connect to the return with two small tubes, so they sit outside the main pipe run. That makes them safer if a part fails and far easier to add to a pool that already runs, since you do not cut the return pipe. In-line feeders are tidy on a new build but harder to service and sit in full flow. If you are adding a feeder to an existing pool, off-line is usually the right call.
Install it last, after the heater, always. This is the one rule that wrecks equipment when people get it wrong. The concentrated, acidic chlorine leaving a feeder will corrode a heat exchanger and eat filter parts if it flows backward through them. The feeder goes at the very end of the return line, downstream of the filter and heater, and it needs a working check valve so chlorine gas cannot creep back to the heater when the pump shuts off.
Only trichlor tabs, and never mix chemicals. Automatic chlorinators are built for 3-inch stabilized trichlor tablets, or bromine tabs in a brominator. Never load calcium hypochlorite or any other product into a feeder that has held trichlor; the leftover residue of the two can react violently. Match the feeder to one tablet chemistry and stay with it. Our tablet picks are in best chlorine tablets.
Match the capacity to your pool size. A feeder that holds 9 pounds of tabs might need refilling only every few weeks on an average in-ground pool, while a small spa feeder holds a handful of tabs. Oversizing is not dangerous, because the dial controls the feed rate, but undersizing means constant refills. Confirm your gallons with the pool volume calculator so you buy the right size the first time.
The dial sets the dose, your test kit confirms it. A chlorinator meters tablets, it does not read your water. Start the control valve low, run the pump on its normal schedule, then test free chlorine after a day or two and nudge the dial. Your target free chlorine depends on your cyanuric acid level, so check it against the chlorine calculator. Feeders are for holding a clean pool steady, not for rescuing a green one.
How we picked
This is a research-based guide comparing off-line and in-line tablet feeders on install type, tablet capacity, feed-rate control, and durability, weighed against a broad set of owner reviews across the established brands. We do not bench-test products, and we take no payment for placement. The install and chemistry guidance reflects well-documented equipment practice, and a commission never changes a pick. Always dose to your tested water and follow the feeder and tablet labels.
Keep your water right, too
Gear handles the cleaning; chemistry is the other half. Useful next: liquid chlorine vs tablets, best chlorine tablets, chlorine calculator, cyanuric acid calculator.
Frequently asked questions
Are automatic pool chlorinators worth it?
For most in-ground pools, yes. An automatic chlorinator holds several weeks of tablets and feeds them at a steady, adjustable rate, so your free chlorine stays more consistent than dropping tabs in a floater and forgetting them. The payoff is fewer chlorine swings and less hands-on dosing. The trade-off is that trichlor tabs slowly raise cyanuric acid, so you still test, and once or twice a season you may need to read how to lower cyanuric acid. If your stabilizer is already high, liquid chlorine or a salt system may suit you better.
What is the best pool chlorinator on the market?
For a standard in-ground pool, the Pentair Rainbow 320 off-line feeder is the most common recommendation: it is safe to plumb, holds up to about 9 pounds of tabs, and rebuild parts are everywhere. The Hayward CL200 is the pick if you want an in-line feeder built into new plumbing, and the Pentair Rainbow 171 is sized for spas and small pools. The right one depends less on brand and more on off-line versus in-line and your pool's size.
How does an automatic pool chlorinator work?
It is an erosion feeder. Water from your circulation system passes through a canister loaded with 3-inch trichlor tablets, dissolving a little chlorine off the tabs on each pass, then carries it back to the pool through the return line. A control dial sets how much water flows across the tablets, which sets the feed rate. Because it works off the tablets you load, it does not create chlorine the way a salt chlorine generator does.
How long does an automatic chlorinator last?
A good feeder body lasts many years, often a decade or more, because it is just a plastic canister with a lid and a valve. What wears out are the o-rings, the lid gasket, the control valve, and the check valve, and those are sold as inexpensive rebuild kits. Rebuilding the seals every couple of seasons keeps an old feeder sealing and feeding like new. A single fill of tablets, by contrast, lasts a few weeks depending on your pool size and the dial setting.
Is there an automatic pool chemical dispenser?
Yes, in a few forms. A tablet chlorinator is the simplest automatic dispenser for chlorine. For pools that dose liquid chlorine or acid, a peristaltic pump system meters liquid from a tank on a timer or a sensor reading. There are also floating dispensers, which are automatic in the loosest sense: they hold tabs and drift, but they do not regulate the rate the way a plumbed feeder does. For steady, adjustable chlorine, a plumbed off-line or in-line feeder is the most reliable.