Controlling Cya

[robquick]

Hi,

I currently use Dichlor only, having read various articles on this site I'm conscious about the impact this could have on CYA levels. I would like to avoid using liquid bleach (long story why) however, if I used Calcium Hypochlorite granules once the CYA exceeded 30ppm would this still achieve the same result in maintaining lower levels of CYA as liquid bleach would ?

I think I read that using Calcium Hypochlorite will slowly increase water hardness levels too, is that correct? If so, do I just keep that in check with hardness reducer?

Any guidance appreciated.

[chem geek]

The following are chemical facts independent of concentration of product or of pool or spa size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

Since one person-hour of soaking in a hot spa without an ozonator needs around 7 ppm FC in 350 gallons, dosing with Cal-Hypo for one person-hour per day would increase CH by roughly 150 ppm per month. So within a couple of months you could risk scaling in your heater, or perhaps even sooner if the pH and TA were higher.

If you want to add chlorine that doesn't increase CYA nor CH and you don't want to use bleach, then you can use lithium hypochlorite, but it's very expensive.

[robquick]

Thanks.

Can I then control (reduce) the calcium levels with hardness reducer?

[chem geek]

There are metal sequestrant products that also sequester calcium to some extent -- they call them scale inhibitors. The only way to reduce the calcium in the water is to replace the water with that lower in calcium, or to use reverse osmosis, or a water softener (ion exchange resin or equivalent), or to use a product like the http://www.hotspring.com/hot-tub-accessories/hot-tub-water-care'>HotSpring® Vanishing Act™ Calcium Remover.