Dichlor

[Nitro]

If you are using Granulated Chlorine (aka Dichlor) to sanitize your hot tub, this is a must read!

Dichlor essentially has two ingredients, Chlorine and Cyanuric Acid (CYA). Almost everyone knows about Chlorine, but few people know about CYA. CYA is used in outdoor swimming pools to limit the breakdown of Chlorine from UV rays. However, it also acts as a Chlorine stabilizer. Basically, it limits the effectiveness of Chlorine, while allowing it to last longer. Think of Chlorine as being a wildfire, and CYA being a water hose. CYA in a sense controls the Chlorine from burning everything up (i.e. you and your tub). Therefore, CYA is a GOOD thing to have in every hot tub and pool (including indoor). The problem comes when there is too much. If there is too much CYA in your tub it will limit the Sanitation (burn) rate too much, allowing certain types of bacteria to grow and form biofilms, namely Pseudomonas Aeruginosa (Hot Tub Itch).

Here are some details:

For every 10 ppm FC you add to your tub using Dichlor, you add 9 ppm CYA. Active Chlorine is a measure of how effective the Chlorine in your tub can kill bugs, and oxidize waste. Active Chlorine is estimated by the ratio FC/CYA. As CYA increases, Active Chlorine decreases (assuming FC remains at normal levels between 1-10). This means every time you add ~11 ppm FC (10 ppm CYA), you drop the Active Chlorine by 1/10th. Let's look at some real numbers. Assume a 350 gal tub with an average of 4 ppm FC added everyday using Dichlor, which is typical. After the first week you will have 25 ppm CYA. After the first month you will have ~100 ppm CYA. That means your Active Chlorine is FOUR times less after a month than it was the first week. So after a month when you soak in your tub with 4 ppm FC, that's equivalent to 1 ppm the end of the first week. After the second month (CYA = 200 ppm), 4 ppm FC is equivalent to 0.5 ppm. Get the picture?

You might be asking why is the industry recommending we use Dichlor which contains CYA. The main reason is that you do need some CYA in your tub. If you have no CYA in your tub the chlorine would be way too strong causing damage to you and the tub. If you had 4 ppm FC in the tub with no CYA, that would be equivalent to ~120 ppm FC with CYA at 30 ppm. That would be a level used in a Decontamination procedure. Not safe for you, or the tub. Some manufactures will even void the warrantee if they find out you were using Chlorine with no CYA. So to try to keep consumers from destroying their tubs and themselves, the industry created a product (Dichlor) with Chlorine and a stabilizer (CYA). However, as we have seen from the facts above, this is not the best solution. As CYA increases in your hot tub, the risk of getting ill (i.e. Hot Tub Itch), and/or having water problems (cloudy water etc.) is much greater.

Some may say they have been using Dichlor for years, and never had a problem. Or, if you change the water evey 2-3 months, you won't have a problem. I say, why risk it, if there's a better solution? If you are using Dichlor in your tub now, a better solution is the Dichlor/Bleach method, pioneered by Chem Geek. All you do is use Dichlor for the first week to build up CYA to 20-30 ppm, then switch to Regular Clorox Unscented Bleach. Bleach has no CYA, so your Active Chlorine will remain the same up until you drain the tub. Other advantages of using Bleach are it's cheap and easy to get. The water will last about twice as long. The only other difference is you need to keep your TA lower (50-60 ppm), and are recommended to add Borates (which actually make the water feel and smell better). If you would like to learn more about this method, check it out HERE.

Lastly, there is no guarantee with this, or any method. All we can do is lower the risk.

[spatech (the unreal one)]

Assume a 350 gal tub with an average of 4 ppm FC added everyday using Dichlor, which is typical.

This is well written and informative except I have to disagree specifically the word typical. IMO it is not typical to add dichlor every day; most people only add 1 or 2 (sometimes 3x per week, per use method), drain every 3 or 4 months and have great success with diclhor because they specifically are not adding it daily.

Now if you are the everyday type user then I can certainly see the increasing CYA coming into play as you explain and in fact I see a lot of people going to Lithium Hypochlorite which is similar to bleach relative to what this discussion is about and sold in a lot of spa stores for the reasons above. I know a few people who use it and swear by it for the reasons you've given and I'm going to have to try it out as well.

[Glid]

I have a chlorine generator in my tub, Onzen. I think the Dichlor/bleach method is really cool, but I can't do this with the generator, right?

[Nitro]

This is well written and informative except I have to disagree specifically the word typical. IMO it is not typical to add dichlor every day; most people only add 1 or 2 (sometimes 3x per week, per use method), drain every 3 or 4 months and have great success with diclhor because they specifically are not adding it daily.

I won't get into a debate about what "Typical" is, but 4 ppm FC per day is not that much. Picture 2 people using the tub for 60 mins, 2 times a week, which is much less than I use mine. Given the rule of thumb, ~7ppm FC per person per hour, that's 28 ppm FC per week (i.e. ~4 ppm FC per day).

However, if someone doesn't use the tub very often, uses MPS to help out and/or changes water often they may not have any problems. I'm just pointing out a better, (i.e. safer) method.

Now if you are the everyday type user then I can certainly see the increasing CYA coming into play as you explain and in fact I see a lot of people going to Lithium Hypochlorite which is similar to bleach relative to what this discussion is about and sold in a lot of spa stores for the reasons above. I know a few people who use it and swear by it for the reasons you've given and I'm going to have to try it out as well.

The problem with Lithium is the cost, which is much higher than Bleach. Otherwise Lithium is a better alternative than using only Dichlor.

[Nitro]

I have a chlorine generator in my tub, Onzen. I think the Dichlor/bleach method is really cool, but I can't do this with the generator, right?

Even if you have a Chlorine Generator, you should still add 20-30 ppm CYA. As a matter of fact, some portable SWCG's use a starter pack conyaining CYA and Borates.

Also, you may need to supplement Chlorine (i.e. Bleach) during high bather loads even though you have the Generator.

[Glid]

I have the opposite, I have low user effect. Real high chlorine levels. Hydrogen peroxide reducer works well, though! CYA is always toward the low end, I will heed the advice.