Dichlor and trichlor both add chlorine and cyanuric acid to pool water. Trichlor commonly provides slow delivery through an approved tablet feeder, while dichlor is commonly sold as soluble granules. Their effects on stabilizer and water balance differ, so they are not interchangeable products.
The comparison that matters after the chlorine is used
| Property | Dichlor | Trichlor |
|---|---|---|
| Common retail form | Granules | Tablets or sticks; granular products also exist |
| Stabilizer contribution | About 0.9 ppm CYA per 1 ppm available chlorine added | About 0.6 ppm CYA per 1 ppm available chlorine added |
| Calcium contribution | Does not add calcium through the dichlor ingredient | Does not add calcium through the trichlor ingredient |
| Water balance effect | Can slightly lower pH and alkalinity | Can drive pH and alkalinity downward more substantially |
| Application | Use the directions for the actual formulation | Match the form and feeder to the label |
The CYA figures compare equal chlorine contributions, not equal scoops or pounds of product. This distinction reverses a common assumption: dichlor adds more stabilizer per unit of chlorine delivered. Trichlor’s slower dissolution does not change that comparison.
Compare cumulative additions, not today’s residual
As a hypothetical example, suppose successive treatments supply a total of 20 ppm available chlorine over several days. Dichlor would contribute roughly 18 ppm CYA; trichlor would contribute roughly 12 ppm. These estimates exclude dilution, other inputs, and losses.
The pool does not need to read 20 ppm free chlorine at any point in that example. Much of the chlorine may already have been consumed. The stabilizer contribution relates to what was added, not the residual remaining today.
Record product use and test cyanuric acid at appropriate intervals. Repeated small additions can matter even when each treatment seems modest. Neither product is a way to avoid stabilizer buildup.
Read available chlorine separately from ingredient purity
Typical dichlor forms supply 56% or 62% available chlorine, depending on hydration. Unmodified trichlor commonly supplies about 90%. Blended products can contain less, so check the actual label.
An active ingredient percentage and an available chlorine percentage describe different things. Do not substitute one for the other in a calculator or cost comparison. Use the field the calculation actually requests.
For cost comparison, divide the package price by the pounds of available chlorine it supplies. Then consider the ongoing CYA and water balance effects. A cheaper pound of product is not necessarily a cheaper treatment routine.
Decide whether you need a treatment or a delivery system
Dichlor granules can suit an approved treatment that calls for a measured addition. A compatible trichlor feeder can provide gradual delivery between checks. Those are different jobs, even though both products supply chlorine.
Don’t put dichlor granules into a tablet feeder unless its instructions explicitly allow that exact product. Pentair’s Rainbow 320, for example, specifies particular slow dissolving tablets. A similar chemical name does not establish dispenser compatibility.
If tablets are dissolving slowly, investigate the delivery problem before changing chemistry. Crushing tablets or adding granules changes the way the device was intended to work. It can also expose you to concentrated chemicals.
Let existing water readings influence the choice
If CYA is already excessive for your system, neither product avoids further stabilizer input. Consider an appropriate unstabilized option within the sanitizer and equipment requirements. The chlorine category guide explains that distinction.
If pH and alkalinity repeatedly fall, review trichlor use alongside other acid inputs. Dichlor’s smaller pH effect does not mean its stabilizer contribution disappears. Choose the whole routine, not one attractive property.
For hard source water, both avoid the calcium contribution of calcium hypochlorite. That does not make every formulation suitable for every surface or treatment. Check additives and application restrictions.
Keep concentrated products separate
Never combine dichlor, trichlor, or another chlorine chemical in a container. Use dedicated clean, dry measuring equipment as directed. Do not consolidate partially used packages.
Changing a feeder’s chemistry requires manufacturer approval, including how existing chemical residue is handled. Calcium hypochlorite must not be substituted into a trichlor feeder. Keep the labels available whenever the product changes.
After an approved treatment or feeder adjustment, verify the pool’s actual free chlorine and pH. Follow the product’s mixing and swimming restrictions. Dissolution speed alone does not establish adequate sanitation.
