Can you put chlorine tablets in the skimmer?
You can, but it is a bad idea, and most pool pros tell you not to. Nothing stops a tablet from dissolving in the skimmer basket, and the chlorine does reach the pool, so people assume it is fine. The catch is that chlorine tablets are trichlor, which is acidic, with a pH down around 2.8 to 3.0 undissolved. Concentrate that acid in the small volume of water sitting in a skimmer and you create a corrosive pocket right at the front of your equipment line.
The reason it causes trouble and a floating dispenser does not comes down to what happens when the pump shuts off. While the pump runs, water flows through the skimmer and carries dissolved chlorine away fairly diluted. When the pump stops, the tablet keeps dissolving into the trapped, still water in the skimmer and the pipe to the pump, and that water turns into a slug of extremely concentrated, very acidic chlorine. The next time the pump kicks on, it drives that slug straight through the pump, the filter, the heater, and the return plumbing.
So the short version is that the skimmer is the one place you should not put tablets, precisely because it sits upstream of everything expensive. A floating dispenser or an automatic chlorinator delivers the same tablets without parking the acid against your equipment.
Why is putting chlorine tablets in the skimmer bad?
Because every time the pump cycles off, the skimmer turns into a tank of concentrated acid. This is the whole problem in one sentence. Trichlor dissolves continuously whether or not water is moving, so in the hours your pump is off, the tablet keeps releasing chlorine and acid into the few gallons of standing water in the skimmer and suction line. That water can drop to a pH low enough to be genuinely corrosive, far below the safe 7.2 to 7.8 range you keep the pool itself in.
Then the pump restarts and sends that acid slug through the system. A single-speed pump on a timer might cycle on and off several times a day, and a slug hits the equipment on every startup. The metal parts in the path, chiefly the pump's internals and the heater's heat exchanger, take an acid bath over and over. Chlorine gas also collects in the dead air space of a skimmer with a tablet in it, and that gas is corrosive to anything metal nearby, including the lid screws and any metal in the skimmer throat.
The dosing is poor on top of the damage. Tablets in the skimmer deliver chlorine unevenly: a strong slug of fresh, acidic chlorine right after the pump starts, then a tapering trickle, then nothing while the pump is off. Compare that with the controlled, steady feed you get from a feeder, and the skimmer looks worse on both counts. If you want the full picture on tablets as a sanitizer, see liquid chlorine versus tablets.
Will chlorine tablets in the skimmer damage your pool equipment?
Yes, and the heater is usually the first thing to fail. Gas and heat-pump heaters run pool water through a heat exchanger that is often copper or cupronickel, and acid eats copper fast. An acidic chlorine slug pushed through that exchanger, cycle after cycle, corrodes it from the inside, and a failed heat exchanger is one of the most expensive repairs on a pool, frequently costing more than a new feeder many times over. This is the single biggest reason not to tablet-chlorinate through the skimmer on any pool that has a heater.
The pump and plumbing take damage too. The acid attacks the pump's impeller, seal, and the metal in the seal plate and any brass fittings, shortening the life of parts that are not cheap to replace. It can craze or soften some plastics over time, degrade the pump lid o-ring, and etch or stain the skimmer itself and the plaster right around the return where the strong chlorine comes back into the pool. None of this happens overnight, which is exactly why people get away with it long enough to recommend it to a neighbor before the bill arrives.
There is a narrow case where the risk is lower: a pool with no heater, a corrosion-resistant pump, and a pump that runs 24/7 so no slug ever concentrates. Even then it still ages the pump seal and corrodes the skimmer, and it still doses unevenly, so it is a false economy against a floater that costs a few dollars. If your pump does not run continuously, see how long to run a pool pump, but the better move is simply to feed the tablets somewhere else.
Where is the best place to put chlorine tablets?
The best place is an automatic chlorinator plumbed into the return line after the heater. An in-line or off-line automatic chlorinator holds a stack of tablets and meters dissolved chlorine into the water on the pressure side of the system, downstream of the pump, filter, and heater, so the acidic water never touches that equipment on its way out to the pool. You set a dial for the feed rate, it stays steady, and you refill it every week or two. The one install rule that matters: an in-line feeder goes last in the equipment line, after the heater, and it needs a check valve so chlorinated water cannot creep back into the heater when the pump is off.
The simplest place is a floating dispenser. A floater costs a few dollars, holds several tablets, and drifts around the pool releasing chlorine as they dissolve. It is a real improvement over the skimmer because the acid is diluted into the whole pool instead of concentrated in your plumbing. The catch is that a floater can get stuck against a wall, the steps, or a vinyl liner and bleach or etch that spot, so keep it moving and fish it out of corners, and take it out before anyone swims.
What you should not do is just toss tablets onto the pool floor. An undissolved tablet lying on plaster or a vinyl liner sits in a puddle of that same acidic chlorine and will bleach, etch, or stain the surface underneath it, and on a vinyl liner it can eat a hole. Tablets are made to dissolve inside a dispenser with water flowing past them, not resting against your pool's surface. For granular shocking or spot dosing, use a fast-dissolving product like dichlor broadcast and brushed in, not a slow trichlor puck.
Are chlorine tablets better in the skimmer or a floater?
A floater beats the skimmer, and an automatic chlorinator beats both. Between the two choices most people weigh, the floater wins easily, because it keeps the acidic water out of your equipment. The skimmer's only advantage is that you do not have to look at a floating duck in your pool, and that convenience is not worth a corroded heater or pump seal. If those are your two options, use the floater.
That said, a floater has real downsides a feeder fixes. A floater doses fastest when it is full and slows as the tablets shrink, so chlorine output drifts over the week, and the floater can park itself in a corner and bleach the liner or sit over the pool light. An automatic chlorinator gives you a dial-controlled, even feed, keeps the acid downstream of your gear, and holds enough tablets to stretch refills, which is why it is the method most pros install.
Whichever feeder you use, remember that trichlor tablets slowly raise cyanuric acid, the pool's stabilizer. That is fine and even helpful up to a point, but if you chlorinate with tablets all season the CYA keeps climbing and eventually throttles your chlorine, so check it with a cyanuric acid test and understand what stabilizer does. When CYA gets too high, switch to an unstabilized chlorine for a while to let it come back down.
How many chlorine tablets do you need, and how long do they last?
The common rule of thumb is one 3-inch tablet per 5,000 gallons of water per week, but treat that as a starting point, not a final number. The right amount depends on your pool's size, the weather, how much the pool is used, and how strong your sun is, so the honest answer is to dose to a target rather than a tablet count. Aim to hold free chlorine at 1 to 3 ppm, test two or three times a week, and adjust how many tablets are in the feeder up or down from there. Work out your water volume with the pool volume calculator and your chlorine needs with the chlorine calculator.
A 3-inch tablet typically lasts about a week in a feeder, dissolving faster in hot, sunny weather and slower when the water is cool or the pump runs less. Two tablets in a floater on a small pool might carry you a week to ten days; a stack in a chlorinator for a larger pool gets refilled on a similar cadence. The variable that changes it most is temperature, since warm water and strong sun pull chlorine out faster, so expect to feed more in July than in September.
The thing tablets cannot do is respond to a problem quickly. They dissolve slowly by design, so they are for steady, hands-off daily chlorination, not for pulling a low reading up fast or clearing cloudy or green water. When you need chlorine now, add liquid chlorine or shock, which act within hours, and leave the tablets to handle the daily baseline. See liquid chlorine versus tablets for which job each one is actually good at.
Frequently asked questions
Does it hurt to put chlorine tablets in a skimmer?
Yes, it hurts your equipment over time. Trichlor tablets are acidic, and in the skimmer they dissolve into a concentrated, low-pH slug of chlorine in the standing water whenever the pump is off. When the pump restarts, it drives that acidic slug through the pump, filter, heater, and plumbing. The heater's copper heat exchanger is the most expensive casualty, but the pump seal, impeller, o-rings, and the skimmer itself all corrode faster. It does not fail overnight, which is why the habit spreads, but it shortens the life of parts that cost far more than a feeder.
Is it better to put chlorine tablets in the skimmer or a floater?
A floater is better than the skimmer. A floating dispenser releases chlorine into the open pool, so the acidic water is diluted into thousands of gallons instead of concentrated against your equipment. The skimmer's only edge is that it is out of sight, which is not worth a corroded heater. Better still is an automatic chlorinator plumbed into the return line after the heater, which feeds tablets steadily and keeps the acid downstream of all your gear. If you do use a floater, keep it from getting stuck against the liner or steps, where it can bleach or etch the surface.
Do I just throw chlorine tablets in the pool?
No. An undissolved tablet lying on the pool floor sits in a pocket of concentrated acidic chlorine and will bleach, etch, or stain plaster, and on a vinyl liner it can eat a hole. Tablets are designed to dissolve inside a dispenser with water flowing past them, so put them in a floating dispenser or an automatic chlorinator, not on the bottom and not loose in the skimmer. If you need to add chlorine in granular form, use a fast-dissolving shock or dichlor broadcast across the surface and brushed in, not a slow-dissolving trichlor puck.
How many 3-inch chlorine tablets should I put in my pool?
A common starting point is one 3-inch tablet per 5,000 gallons of water per week, so a 15,000-gallon pool might run about three tablets in the feeder. Treat that as a guess to adjust from, not a fixed dose, because sun, heat, and bather load change how fast chlorine burns off. The real target is holding free chlorine at 1 to 3 ppm, so test a few times a week and add or remove tablets to stay in that range. Use the pool volume calculator to confirm your gallons and the chlorine calculator to dial in the amount.
How long will 2 chlorine tablets last in the pool?
Two 3-inch tablets in a floater on a small pool usually last about a week to ten days, but it varies a lot with temperature. In hot, sunny summer water they dissolve faster and may be gone in under a week; in cool water with the pump running fewer hours they last longer. Rather than counting days, watch your free chlorine reading: when it starts dropping below 1 to 3 ppm, it is time to add more. Keeping the pump running on a sensible schedule also keeps the feed steady.