Di-Chlor vs Cal-Hypo : What is best to shock your pool?

Blake from PoolSupplyWorld explains the differences between Di-Chlor and Cal-Hypo. Both can be good options to chlorinate or shock your swimming pool, but you should understand the side-effects.

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Video Transcription:

Hey, Blake here from PSW

Today we’re going to talk about chlorinating your swimming pool with either Di-Chlor or Cal-Hypo because they are both good options, but they also both have some side effects. I want to make sure you are aware, so you can pick the right one for your pool.

Let’s start with Di-Chlor first

The scientific name is Sodium Dichloro-S-Triazinetrione, which is a quite the mouthful.

Di-Chlor is 55% free and available chlorine.

The Di-Chlor that we sell is 99% Sodium Di-Chlor which means there is 54.8% available chlorine that is going to be able to fight algae and breakdown organic matter in your swimming pool.

However, there is a side effect.

Di-Chlor contains Cyanuric Acid. CYA acts like sunscreen for the chlorine in your swimming pool. It helps preserve it.

There are two ways that chlorine in your pool can get used up. It can either be consumed by breaking down organic matter like algae, or it can burn off from the sun. So the Cyanuric Acid acts like sunscreen and helps prevent the chlorine from burning off from the sun. However it also reduced the effectiveness the chlorine has to be able to fight algae.

So you want a little bit in your pool.

With a salt water generator (SWG) you want to have 60-80 parts per million (ppm). Without a salt water generator, you want to be between 30-50 ppm. This is important to know because when using Di-Chlor, for every 1 ppm of free chlorine you add, you are also adding 0.9 ppm of CYA. So if you are near the upper limits [of recommended levels], you probably want to stay away from Di-Chlor.

Which brings us to Cal-Hypo.

Cal-Hypo is also called Calcium Hypochlorite, and is 99.18% free and available chlorine. The Cal-Hypo [shock] we sell is 68% calcium hypochlorite, which means 67.4% available chlorine that can fight algae in your swimming pool. As you can see, this is a little bit higher than the Di-Chlor when you are looking at even weights. But, like Dichlor, Cal-Hypo does have a side effect.

Cal-Hypo has calcium in it. If your calcium levels are already high, you probably want to stay away from it.

The ideal Calcium Hardness (CH) level for a vinyl pool is anywhere between 0 and 350 ppm. You don’t actually need calcium, but it’s not going to hurt anything as long as it’s not over 350.

The ideal CH level for a plaster or gunite pool is between 250 and 350 pp. That is the sweet spot. If you are too high, you could get calcium scaling, which is no fun.

This is important to know because for every 1 ppm of FC you are adding (with Cal Hypo), you are increasing your CH by 0.7 ppm.

Now, if you are wondering what to use…

It comes down to 3 simple steps.

First, you should test your pool water. We recommend the TF-100 by TFTestkits, but we sell several different test kits that are going to allow you to test your CYA, CH, and other chemical levels.

Once you test your water, take notice of your CYA and CH levels, and compare them to the recommended levels. Based on that, you can make your decision. So if your CH is really high, and your CYA is low, then you can use Di-Chlor (and visa versa).

If your CH is already pretty high, and your CYA is also pretty high, you actually have another option. That is Liquid Chlorine (or Sodium Hypochlorite). That is going to be 95% free and available (chlorine).

You can actually use bleach from your local store if you want to, but make sure you are aware of the strength. You might buy bleach that is “6% strength” but what that actually means is 5.7% is available chlorine to fight algae in your pool.

Now this looks like a big difference between the 54.8% and 67.4% from Di-Chlor and Cal-Hypo. The plus side is that it will not add CYA or CH. It will only add free chlorine to your swimming pool.

That’s pretty much it. If you have any questions you can comment down below the video, or email us directly at [email protected]

Happy swimming!

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