Cal Hypo

[Rickmart]

I've been using Cal Hypo shock in my inground, vinyl pool. The shock seems send my ph all over the place. I would appreciate suggestions on the most preferred shock. Thanks.

[aylad]

Hi Rickmart, and welcome to the forum!

Keep in mind that "shock" is actually a verb, something you do to the pool, rather than a noun, something you put into the pool. To shock a pool simply means to raise your chlorine to an elevated level based on your CYA readings. You can use cal-hypo like you have been, dichlor powder, or liquid chlorine (bleach).

I don't think it's the cal-hypo that's making your pH fluctuate, because it's usually fairly pH-neutral. Often if the pH flucutates too much, you need to change your TA values, but without actual numbers to look at we can only guess at the problem. Can you post a set of test results (taken with a drop-based kit, no strips!!) for us to look at? How are you testing your water? Define "all over the place"?What form of chlorination do you use on a daily basis?

We'll be glad to help, we just need a little more information

[Rickmart]

After shocking, the ph rises. Everything else stable. I chlorinate with Biogard smart sticks. My water clear and beautiful, no clouding. I use Biogard Lo n Slo to bring ph down.
I am really going to like this forum. Thanks

[aylad]

Without a set of test results to look at, I'm afraid we won't be of much help. If you use smart sticks, which are trichlor, they drive pH down. Then if you shock with cal-hypo, the pH probably rises a little with it. Again...we need to look at your TA, and if you can tell us what range your pH stays in (lowest and highest) then maybe we can give you better info.

[Watermom]

Also, please put your pool's information in our pool chart. It makes it easier for us to help you.

Pool Chart Entry Form
Pool Chart Results

[PoolDoc]

I've been using Cal Hypo shock in my inground, vinyl pool. The shock seems send my ph all over the place.

If you've been using Bioguard Stingy Sticks, you probably have been listening to them on what your pH needs to be. Get a good test kit, test your pool, tell us what you find, and THEN tell us what your pH readings are doing. It may well be that your "problem" is actually no problem at all.

However, it's possible to use cal hypo with very little pH movement. I used it continuously for 3 years on an indoor commercial pool, and during that entire period used only 1 - 2 gallons of muriatic acid!

[waterbear]

After shocking, the ph rises. Everything else stable.

After shocking the chlorine level also rises and high chlorine can interfere with the pH test and cause it to read high when it is not. This is a chemical interference caused by the phenol red pH indicator being converted into chlorphenol red, which responds to a much lower pH range than phenol red so it seems as if your pH has risen when it has not. If the pH is normal at normal chlorine level and high at shock chlorine level then it is simply this interference and the pH is not really high. Exactly how are you testing your pH? Some pH tests are more susceptible to this problem than others and ti can occur at chlorine levels as low as 3 ppm but most good test kits (such as ones from Taylor and LaMotte) do not exhibit this interference until about 10 ppm chlorine (what is commonly considered "normal" shock level by pool stores).

FWIW, Lo n Slo is just sodium bisulfate or 'dry acid' and there is nothing special about it. Many companies sell dry acid under various names and they are all the same thing, marketing material aside. We actually prefer muriatic acid in the forum because it does not add sulfate to the water but dry acid is certainly acceptable to use unless you have a SWCG.