Choosing whether to use trichlor or dichlor in your pool can seem like a daunting task for new pool owners. While trichlor and dichlor are both suitable options and have similarities, they have key differences. Which chlorine will make a better choice over the other? Find out here.
For daily chlorination and maintaining your free chlorine levels, trichlor is best. It is slow dissolving for sustained chlorination and contains stabilizer. For quick boosts to cyanuric acid (stabilizer) and chlorine, dichlor is best. Dichlor has more stabilizer in it than trichlor and will raise cyanuric acid quickly.
The best choice for pool owners will depend on the current level of cyanuric acid (stabilizer), pH of pool, calcium levels, chlorine levels and the type of water you have. It is important to know what you are trying to achieve and the pros and cons of each before selecting your chlorine.
Let’s look at dichlor and trichlor in more detail.
Article Contents
What is Trichlor (trichloro-s-triazinetrione)?
- 3" chlorinating trichlor tablets
- Contains stabilizer to protect against sunlight
- Prevents algae and kills harmful bacteria
Trichlor is a dry solid chlorine with 90% available chlorine. This is the highest available chlorine content of any chlorine that you can get.
Due to its high concentration of chlorine, you can use less of it than you would with other products, and it is one of the least expensive chlorine products you can get for your pool.
Trichlor is typically found in tablet form meaning that you can place however many tablets that you need to chlorinate your pool in a floating container, and it will sanitize your pool to your exact needs.
Trichlor is a mixture of chlorine and cyanuric acid which makes it stabilized chlorine. What this means is that it contains cyanuric acid for sun protection. This sun protection is important because it ensures that sunlight and bacteria won’t use up all the available chlorine too fast.
Trichlor can be used in both pools and spas to sanitize. When the trichlor dissolves into the water, it turns into hydrochloric acid.
When this happens, the acid attaches to bacteria and begins to kill it. Trichlor works similarly to other products on the market, but it does so in a more efficient manner.
A strong benefit of trichlor is that it is self-maintaining. This means that you can set it and forget it (until it runs out, of course). The tablets dissolve slowly, so you won’t have to add additional chlorine into your pool every day.
A few things to keep in mind when using trichlor is that it can actually raise your cyanuric acid (CYA) levels too quickly. Trichlor will raise your cyanuric acid by 0.6ppm for each 1.0 ppm of chlorine added, so keep that in mind. That amount is significant and will build up over time.
Another thing to keep in mind is that if not used correctly, tri-chlor can actually stain or rust your pool.
When using trichlor, you may need to boost your pH to keep it at a desired level of 7.2-7.8. Trichlor is acidic and has a pH of about 3. As a result, it will lower your pool’s pH slightly. Having pH increaser on hand is a good idea in case you need to boost it back up.
While Trichlor is great for daily chlorination, it is not a great product to use when shocking your pool or quickly raising chlorine or stabilizer levels. Trichlor is slow dissolving and when shocking your pool, you want a product that will dissolve quickly and boost chlorine levels fast.
Pros and Cons of Trichlor
| Pros | Cons |
| Strongest chlorine concentration you can buy | Can rust or stain pool surfaces |
| Tablets make it easy to measure and maintain your pool | Can cause a chemical reaction (explosive) if mixed with calcium hypochlorite |
| Slow Dissolving and lasts longer than other options | Lower pH |
| Great for daily chlorination | |
| Generally costs less than Dichlor |
What is Dichlor (Sodium Dichloro-S-Triazinetrione)?
- 99% sodium dichlor
- Lasting longer than other supplies
- Dissolves quickly
While dichlor can be found as a tablet, it is more commonly seen in granular form in either small bags or large tubs. Free chlorine in dichlor is about 55%-62% and it contains a pH of about 6.5.
When using dichlor to sanitize your pool, it is commonly pre-dissolved into a bucket and dumped into the pool. When used in granular form, dichlor is fast dissolving and goes to work quickly. Tablets can leave behind residue so the power or granular form is better for this reason.
Much like trichlor, dichlor also contains cyanuric acid. Cyanuric acid is a good thing as it helps the chlorine do its job – but too much cyanuric acid (aka stabilizer) is a bad thing. Dichlor has even more cyanuric acid than trichlor so it should only be used when cyanuric acid levels are low.
Dichlor is not a great choice for daily chlorination of your pool for this reason. Too much cyanuric acid makes the chlorine not work as effectively meaning you must add more chlorine to compensate. More dichlor results in more cyanic acid.
Not too sure on how much stabilizer you need and what it is? Check out our article What is Swimming Pool Stabilizer & When To Add It
Dichlor is recommended for use if you have cyanuric acid levels that are between 30ppm and 40ppm. This is considered low and dichlor will help raise your CYA while also chlorinating your pool.
Pros and Cons of Dichlor
| Pros | Cons |
| Fast dissolving for when you need to quickly raise chlorine and cyanuric acid | Can be expensive compared to Trichlor |
| Neutral pH | Doesn’t always come in tablets – and tablets can leave residue in pool |
| Comes in small bags or containers | Contain high levels of stabilizer |
| Can last a long time when stored |
Differences Between Trichlor and Dichlor?
Trichlor affects a pool’s pH and has a high chlorine saturation at around 90%. Trichlor usually comes as a tablet that dissolves into your pool slowly over time.
Trichlor requires no measuring and is self-maintaining making it ideal for most pool owners. Simply place the correct number of tablets into a floating dispenser and let it work.
Dichlor on the other hand can come as a tablet but is usually found in granular form and comes in a bag or tub. Dichlor also has a lot less chlorine and a lot more stabilizer or cyanuric acid. It does not impact the pH of your pool and it dissolves very quickly.
Check out the chart below for a full breakdown of the differences in trichlor vs dichlor.
Trichlor vs Dichlor Specifications
| Trichlor | Dichlor | |
| Form | Tablet | Granular |
| Available Chlorine | 90% | 55-62% |
| pH | 3 | 6.5 |
| Rate of Dissolve | Slow (days) | Fast (hours) |
| Pool Stabilizer | Cyanuric Acid | Cyanuric Acid (More than trichlor) |
| Ideal for Daily Chlorination | Yes | No |
| Ideal for Shocking | No | No |
| Cost | Cheaper than Di-chlor | More than Tri-chlor |
| Where to Buy | Check price | Check price |
Should You Use Trichlor or Dichlor?
The answer to the question of if you should use trichlor or dichlor is dependent on what you are trying to achieve with your pool.
When looking to maintain your current chlorination levels of your pool, trichlor is the better option. Trichlor dissolves slowly and is more of a maintenance free option. Unlike liquid chlorine or calcium hypochlorite (cal-hypo), you won’t need to add trichlor multiple times per week.
Trichlor is also a great option to maintain chlorine levels when you’re away or on vacation.
If your pool is low in both chlorine and cyanuric acid, dichlor is the better choice. Because it dissolves quickly, dichlor will raise both the CYA and chlorine levels quickly.
However, it is not recommended for daily chlorination since it will raise stabilizer levels as well as chlorine.
How Many Trichlor Tablets Should You Use?
The number of trichlor tablets needed for the average pool will be between 1 and 3 per week. A 3″ 8-ounce tablet will increase Free Chlorine (FC) levels by about 4.5 ppm and Cyanuric Acid (stabilizer) by 2.8 ppm.
Many factors will affect the number of tablets needed including the pool’s volume, if you use a pool cover, if the pool is in the sun or shade, number of bathers using the pool and weather conditions.
To correctly determine how many trichlor tablets you need you’ll need to test your water frequently. Based on your testing, you can then adjust the frequency and number of tablets you add to your pool.
You can test your pool water with a quality test kit like this.
- Tests total alkalinity, free/combined chlorine, cyanuric acid, calcium hardness & pH
- Extremely accurate (better than test strips)
- For pools & spas
Should You Use Trichlor or Dichlor to Shock Your Pool?
Trichlor or Dichlor are not good options for shocking your pool. Shocking your pool requires you to add 10X more free chlorine than the combined chlorine level. Trichlor is a slow dissolving product and because of this, it will not raise the chlorine levels sufficiently for shocking.
Dichlor is not a good option because of the high levels of cyanuric levels in your pool. If you use dichlor for shocking, you’ll likely end up with cyanuric acid levels which are too high. And as a side point, cyanuric acid also decreases the chlorine’s effectiveness. This defeats the purpose of shocking.
If you are looking to shock your pool, calcium hypochlorite is a much better option for some pool owners. Calcium hypochlorite is unstabilized, meaning it contains no cyanuric acid, so it will not raise your cyanuric acid levels and will raise your chlorine levels quickly.
Related Reading: Which Pool Shock Should You Use? (answered!)
Can You Mix Trichlor and Dichlor
You should NEVER mix dichlor with trichlor or different chlorine types. When mishandled, these products can become unstable and dangerous and could result in toxic gases, explosions, or fires. It is also worth noting that misuse can lead to staining of your pool surfaces.
Both trichlor and dichlor should be handled with great care. You should be careful not to let either of these chemicals come in contact with each other. Follow safety information on the product labels and store in a cool, dry place. Mixing these products directly with other chemicals can also result in a chemical reaction.
The video below is a news story showing what happened when pool owners mixed two different chlorine types – it caused an explosion.
Related Reading: Can You Mix or Switch Chlorine Types? (Answered!)
Final Thoughts
When choosing between trichlor and dichlor, it is important to know what you are going to be using it for. Trichlor slowly dissolves and is ideal for daily chlorination, is cheaper and is easier to maintain. Trichlor is more of a set and forget method with its tablets.
Dichlor is better for raising your levels of chlorine and cyanuric acid quickly.
Both trichlor and dichlor contain cyanuric acid, which is needed in your pool, but if your levels get too high, it makes your chlorine ineffective, so be sure to keep an eye on your CYA levels.
Neither makes for a great shock, but dichlor works in a pinch. Calcium hypochlorite is better suited for shocking.
Related Reading: Which Chlorine to Use for Inground Pools?
