Liquid Chlorine vs. Granular Chlorine - Which Is Better?
There are many forms of chlorine available for use in your swimming pool.
Because pool chlorine can come as a solid or liquid, in stable and unstabilised forms, and is sold as a variety of chemical compounds, working out which product you actually need for your pool can be confusing.
In this article, we will discuss the main uses of liquid chlorine vs granular chlorine, various chemical compound names you may encounter, and review the pros and cons of liquid and granulated chlorine for various uses.
Liquid Chlorine vs. Granular Chlorine - Main Differences
Both liquid chlorine and granular chlorine are effective sanitising products for your pool that can be used for oxidising bacteria, algae and other organic material. They can both be used regularly to maintain a free chlorine level, or for shocking your pool.
Despite commonly being called ‘chlorine’, these products do not actually contain pure chlorine molecules, which are actually a very toxic and dangerous gas when found unbonded at room temperature.
Regardless of the specific formula used, these products contain compounds that form hypochlorous acid (HOCl) once introduced to your pool’s water.
Granular chlorine, sometimes referred to colloquially as powdered chlorine, consists of chlorine containing compounds that are solid at room temperature. It is widely used as a pool shock product and some forms are suitable for regular maintenance.
Many granulated chlorine products need to be mixed before they can be added to your pool, and must be added to a bucket that is full of water.
It is dangerous to add chlorine to the bucket first followed by the water, because you run the risk of allowing chlorine gas to be produced. If the bucket is not full of water, there will not be enough liquid to trap any released gas, allowing it to enter the air you breathe.
Granular chlorine typically consists of one of the following chemicals:
- Calcium hypochlorite
- Trichloroisocyanuric acid
- Sodium dichloroisocyanurate
Of these, only the calcium hypochlorite is unstabilised chlorine (ie. does not contain cyanuric acid).
Liquid chlorine is always in the form of a solution of sodium hypochlorite, which is a liquid at room temperature. This is the same chemical found in household bleach.
Liquid chlorine is much less concentrated than solid forms, meaning that you need to dose a fair bit more to achieve the same dose of free chlorine in your water.
Liquid chlorine can usually be added to your pool’s water without needing to be mixed.
Despite being weaker than its granular counterparts, liquid chlorine is still several times more concentrated than household bleach, so care must be taken when using it.
Formation of chlorine gas is still a risk with liquid chlorine, as well as the risk of it splashing back onto you as you pour it into your pool. Be sure to always wear protective gloves and glasses when handling liquid chlorine.
Skin contact with concentrated liquid chlorine can cause severe chemical burns, which have similar effects on flesh as frostbite.
What About Lithium Hypochlorite?
Some pool owners may also be familiar with granular or liquid chlorine that is composed of lithium hypochlorite. While this compound was once very prevalent in the pool supply market, in recent years it is losing favour to calcium hypochlorite, which is cheaper to produce.
This is mostly caused by the high demand for lithium-ion batteries in recent years.
Liquid Chlorine - Pros and Cons
Pro #1 - Easier to mix into your pool
Liquid chlorine doesn’t require pre-dissolving into a bucket before adding it to your pool - it’s already in liquid form!
Pro #2 - No stabiliser or calcium addition
Many pools suffer from having too much cyanuric acid (stabiliser) which actually reduces the effectiveness of their chlorine.
Other pools suffer from excess calcium in their water, which, when combined with high alkalinity and pH, contributes to calcium scaling and deposits on your pool surface.
Thankfully, liquid chlorine doesn’t add any stabiliser or calcium into your pool, only sodium, which is relatively harmless.
Con #1 - More dangerous than granular chlorine
When dosing liquid chlorine, you have to take great care to avoid any splashback of chlorine onto your skin or eyes.
Any contact with skin or eyes could deal serious damage - something that can be avoided by using granular chlorine.
Con #2 - Dangerous Good
Unlike granular chlorine, liquid chlorine is considered a dangerous good in Australia, which means that it can’t be sent in the mail.
It can’t be purchased online - instead you’ll need to pick it up at a local hardware or pool supply shop.
Con #3 - Actual chlorine concentration not disclosed
Unlike granular chlorine, most manufacturers of liquid chlorine do not disclose the actual concentration of sodium hypochlorite in their product.
This means that you can’t compare one product to another, or compare liquid products with granular products properly.
In fact, many people who get their chlorine from Bunnings have recently complained that the chlorine there has been watered down compared to when they previously bought it.
As the manufacturer doesn’t list a chlorine concentration, they are free to do as they like. On their chemical safety data sheet, they just list a concentration between 10-30% for sodium hypochlorite.
Granular Chlorine - Pros and Cons
Pro #1 - Comes in stabilised and unstabilised forms
With granular chlorine, you can choose from types that contain cyanuric acid (dichlor and trichlor), and those that don’t (cal hypo), which gives you more flexibility.
Cyanuric acid protects free chlorine molecules from degrading in the sun, making it a necessary component for the chlorine used in regular outdoor pool maintenance.
However, it is not necessary to always use stabilised chlorine because this can lead to a buildup of excess cyanuric acid, which comes with its own problems.
Never mix different types of chlorine products together.
Pro #2 - Easier and safer to handle and store
Unlike liquid chlorine, granular chlorine is less likely to splash back onto your eyes and skin when you add it to your pool.
It also keeps better and has a longer shelf life, which means that you can save money by buying it in bulk and using it slowly over time.
Pro #3 - Can be purchased online
Granular chlorine is not considered a Dangerous Good in Australia, so you can purchase it online and have it sent to your door.
This allows you to shop around and get the best price.
You can, of course, still purchase it in-store if you wish.
Pro #4 - Available chlorine concentration clearly disclosed
This is another major benefit of granular over liquid chlorine.
All manufacturers of solid chlorine clearly state the concentration of available chlorine (in grams per kilogram) that their product contains.
This means that you know exactly what you are getting, can compare different products easily, and can calculate your chlorine dose quickly. Use a chlorine dose calculator to assist here.
You also don’t have to worry about the manufacturer slowly diluting their product over time to save money.
Con #1 - Granular chlorine will add to stabiliser or calcium levels
The only real downside of granular chlorine is that it will either increase your stabiliser concentration (if using stabilised chlorine), which can be bad if your stabiliser is above 50 ppm, or it will increase your dissolved calcium concentration.
Because high cyanuric acid can be problematic, I tend to recommend that people use calcium hypochlorite. In saying that, you do need to keep an eye on your calcium concentration.
Excessively high calcium concentrations, when coupled with high alkalinity and pH, will result in calcium scale and deposits forming on your pool surface. This is a pain to deal with.
However, the amount of calcium added from regular calcium hypochlorite additions is actually quite minimal. For some people with soft water, this extra calcium can actually be beneficial, and save you from having to add calcium yourself to avoid pool surface etching.
Liquid chlorine and granular chlorine are both great options for sanitising your pool. Both can be used as pool shock or for regular maintenance.
Deciding which one is better can depend a lot on your situation.
Generally speaking, I recommend granular chlorine as it’s easy to handle, easy to purchase, convenient and the chlorine dose is clearly disclosed by the manufacturers. In particular, I recommend calcium hypochlorite.
Do you have any questions about liquid vs granular chlorine? Let us know down in the comments!
A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.