In-line or off-line chlorinator?
Choosing between them is a plumbing question, not a performance one. An in-line feeder becomes part of the return pipe, so it wants a length of straight pipe after the filter and the heater to live in, and it is the neater install when the pad is being built or repiped. An off-line feeder sits on the deck beside the equipment and takes a small hose off the pipe through a clamp, so it goes in without cutting the return apart, which is usually why people choose one. Both meter the same tablets through the same kind of dial.
What size chlorinator does my pool need?
Size on gallons, then on how often you want to open the lid. Bodies here run 4.2 lb for an above ground pool, 9 lb for most inground pools, 10 lb on the Perform-Max feeders, and 15 lb and up on the commercial Rainbow bodies. Published ratings on this page run from 18,000 gallons at the small end to 322,000 at the commercial end. A feeder loaded lighter than its rating is not a problem, so when a pool falls between two bodies the larger one simply means fewer trips out to refill it.
Does a tablet feeder work behind a variable speed pump?
Only above the flow the feeder needs, and almost none of them publish one. An erosion feeder works by pushing pool water across the tablets, so a pump idling on a low overnight speed can leave the body sitting in nearly still water and dosing nothing, which looks like a broken feeder and is actually a pump schedule. The CMP PowerClean Ultra VS is the one body here that states its window, 20 to 50 GPM with 20 as the floor. Any feeder behind a variable speed pump wants a run each day fast enough to feed it.
Can I load cal hypo tablets into a trichlor feeder?
No. They are two different chemistries and mixing them, or loading one into a body still carrying the other's residue, is a genuine hazard rather than a warranty technicality. Cal hypo needs a feeder built for it: the CCH Endurance body on this page is the one here, and its own specification names the tablet it takes. If a feeder has ever held trichlor, it stays a trichlor feeder. Nobody in this collection publishes a statement that any body takes both, and that silence is the answer.
How is this different from a salt system?
Where the chlorine comes from. A feeder meters out chlorine you bought, as tablets or as liquid from a drum, and it runs on water flow with no power at all on most bodies. A salt system makes chlorine on site by passing current through salted water, so it needs a cell, a power supply and salt in the pool, and the cell is a wearing part with a life in hours. Shoppers type chlorinator for both. Salt generators, cells and salt system parts each have their own page here.
Why not just drop tablets in the skimmer?
Because of what happens when the pump stops. Trichlor tablets dissolve into water that is strongly acidic, and in a skimmer that water sits against the pump housing, the seal and the heater exchanger every hour the pump is off, concentrated rather than diluted into the pool. A feeder puts the tablets downstream of all of it and doses on the return instead. If a basket is the only place you have, the tab holder on this page at least keeps the tablets out of the impeller, but it does not change the chemistry.
Tablet feeder or a chemical feed pump?
Tablets are the residential answer and liquid is the commercial one, and the split is about control. A tablet feeder is a dial and a body full of slow dissolving pucks: cheap, simple, no power, and it doses roughly. A peristaltic pump squeezes liquid chlorine or acid out of a drum at a set rate, from a few gallons a day up to 170, and it can be switched by a controller reading pH and oxidation reduction potential. Pick the pump when something has to hold a target rather than stay in a range.
