So, this is an excellent question that doesn’t make a whole lotta sense. We will delve into why and hopefully by the end of this article I will have helped you understand more about the different types of chlorine and their intended uses. Let’s jump right in!
Why Use Chlorine at All?
Think of a swimming pool as a piece of mother nature in captivity, because that is exactly what it is. Your pool water will try to behave much like it does in the wild. Since it can’t roam free, pick up minerals and keep itself clear, we are left with this honor. Swimming pool water needs several things to be safe. Circulation and proper chemical balance are key. We have to sanitize our water to keep people safe, fight off algae and keep the water clear and inviting.
Chlorine is the most widely used form of a swimming pool or spa. It comes in many-a-forms.
Chlorine tablets are used to maintain a chlorine residual of 1 part per million (ppm) or above. They are not designed to raise chlorine levels. How it works is we first create a chlorine reserve by adding liquid or granular chlorine. Then the tablets help maintain that chlorine bank throughout the week. Chlorine tablets are most commonly a tri-chlor formula. They do make calcium hypochlorite tablets, but these are not as common and even require a special floater. Trichlor tablets are a form of stabilized chlorine. This means they contain a component called cyanuric acid.
A decent level of cyanuric acid is recommended in swimming pools to help prevent chlorine from immediately burning off in the sun’s rays. We aim for 30-50 ppm in a traditionally chlorinated pool and 50-60 ppm for salt-chlorinated pools. Anything under 99 ppm is fine. When the cyanuric acid exceeds this level, it actually works against you by making the chlorine less efficient. To what degree it is less efficient cannot be measured so the only solution to lower CYA in swimming pools is to drain and add fresh water. Cyanuric acid does not evaporate. It is only lost by splash out and water replacement.
We recommend removing the chlorine tablets in the Winter so as not to increase our cyanuric acid levels too rapidly, causing a need for a premature drain. In the colder months, the liquid or granular chlorine you add is generally enough to carry your swimming pool’s levels throughout the week.
Liquid chlorine is probably the easiest type of chlorine to use. It is sodium hypochlorite and typically comes in 10-12 % strength. You can add the liquid chlorine directly to the swimming pool water and go in after just one hour of circulation. Keep in mind that liquid chlorine is mostly made of salt, so you increase your total dissolved solids rather quickly. Every chemical leaves something behind. This adds to your swimming pool water makeup. Can you shock your pool with liquid chlorine? Absolutely. Shock is actually a method, rather than a product. This can get confusing as some products are labeled “shock”. This just means if you intend to shock your pool, this product is a viable option. You can use “shock” as a maintenance dose, or add extra to “shock” the pool. When we shock our swimming pools we add enough chlorine to reach what is known as a chlorine break point. This oxidizes contaminants out of the water, gets rid of combined chlorine (which is the non-killing form of chlorine, aka chloramines), and leaves you with a nice chlorine back. Depending on the reason you are shocked will determine the amount.
f we are just trying to clear up chloramines it would be substantially less than say if someone pooped in the pool or even combatted an algae bloom. In simple terms, shocking the pool just means more than a maintenance dose. This can be done with liquid chlorine or granular.
Di-Chlor is another form of stabilized chlorine, which means it contains cyanuric acid. You don’t want to use this form of chlorine in conjunction with tablets as it will raise your CYA too much. Di-Chlor comes in a powdered form and is usually around 55% chlorine. It is great for special vessels such as salt pools, spas, vinyl-lined pools, and above-ground pools. Can you shock with di-chlor? Absolutely. It has the same principle we discussed above.
Calcium Hypochlorite is designed for in-ground, plaster pools. It is the strongest chlorine with percentages ranging from 68% and up. This is what is usually packaged as “shock”. Like any chemical, it leaves something behind. In this case, calcium. It is not recommended for regular use on a salt pool although using it sporadically for an emergency won’t kill your calcium level. Cal-hypo is also a granular chlorine that can be added directly to the pool. Some pool pros say it is ok to put in the skimmer. Ask 5 different pool guys, get 5 different answers. Just keep in mind after adding ca-hypo, the pool needs to circulate for a minimum of 4 hours, or until the chlorine level is back in a safe range of 2-5 ppm. So can you shock with cal-hypo? Absolutely.
Trichlor is not limited to tablet form. It is also available in granular form. It can be great at treating algae. Bear in mind it is still a stabilized form of chlorine so you are adding cyanuric acid to your swimming pool if using this. Percentages of trichlor are all over the map so always read every product label instructions carefully and use the proper personal protective equipment (PPE). Can you shock with trichlor? Absolutely.
Salt Water Pools
A saltwater pool is still a chlorine pool. You are just making your own through a process known as electrolysis. You can actually shock, or super chlorinate, from your salt system. Keep in mind this often requires 24 hours of pump run time so many pool owners opt for liquid since it is composed mostly of salt anyway. Can you shock a salt water pool? Absolutely.
Hopefully, you found this piece helpful in determining which type, or types, of chlorine is right for you and your swimming pool’s needs. See you poolside!