Rainbow Chlorinator Tips and Tricks: Maintenance Made Simple

Pentair Rainbow chlorinators are some of the most common tablet feeders on pool pads, and for good reason: they are reliable, familiar to pool service pros, and easy to keep running with basic maintenance. I prefer the Rainbow line over many alternatives because the design is serviceable in the real world, especially when you are moving fast on a route. The big rule that frames everything is tablet compatibility and safety. These are trichlor tablet chlorinators only. Never use cal-hypo tablets in a trichlor feeder, and never switch chemicals in an old unit with residue inside. Mixing trichlor and calcium hypochlorite can cause a violent reaction, including an explosion, and it is not worth the risk.

There are two main styles you will see: the offline Pentair Rainbow 300 series (often recognized by the black tubing) and the inline Rainbow 320 series that is plumbed directly into the return line. I do not treat one as universally “better,” but they fail in different ways. Offline units are popular for retrofits because you can add them without cutting in a new section of plumbing, while inline units are commonly installed during the build. No matter which model you touch, placement matters for pool maintenance and equipment protection. Install the chlorinator after the heater and downstream of sensitive equipment so acidic, highly chlorinated water does not backflow into the heater and damage components.

The most serious field problem is opening a chlorinator and getting hit with toxic fumes. When tablets do not fully dissolve and an air gap forms, the trapped gases can be overpowering. The practical habit is simple: do not hover over the lid. Open it at arm’s length, set the lid aside, and step away for 30 to 60 seconds. Let it vent, listen for gurgling as air moves through the line, then look in from above without leaning into the opening. If you see a stack of partially dissolved trichlor tablets, close it back up and troubleshoot the cause rather than breathing the fumes or doing a “sniff test.”

On the offline Rainbow 300 series, the usual culprit is the feed check valve elbow that clogs with trichlor residue. When that little check valve ball sticks, water flow through the feeder drops and tablets stop dissolving, which increases fume buildup. The common replacement part is the R172061 feed check valve 90 degree elbow, and replacing it is typically faster than trying to clean it. Turn off the system, secure the lid, flip the feeder, and remove the black tubing at the bottom. Inspect for damage, trim cracked tubing if needed, and reinstall with the new elbow. Inline Rainbow 320 units do not rely on the same check valve elbow, but they can trap air; a useful trick is to start the system with the lid off so the canister floods completely, then close it. Also pull and clean the bottom screen using a safe tool like oven tongs.

Two more frequent service calls are stuck lids and brittle tubing. A lid that feels glued on is usually a swollen lid O-ring that has expanded from heat and chemical exposure. The replacement O-ring is R172009, and lubrication helps; use a silicone-based lube such as Magic Lube so the lid threads smoothly and seals without binding. For removing a jammed lid, a long, sturdy pair of 16.5-inch tongue-and-groove pliers (large channel locks) can provide a controlled wedge and enough leverage without destroying the lid. The black tubing itself is an Achilles heel in direct sun: it becomes brittle, cracks easily, and can create a major leak that drains the pool. Squeeze-test the tubing during regular pool service; if it crackles, fades, or feels stiff, replace both inlet and outlet lines together. Keep spare tubing (R172023) and consider carrying the rebuild kit R172064 for connectors, O-rings, and small parts so you can fix leaks on the spot and keep the chlorinator running for years.