How does CYA keep coming back?

[Guest]

I have a spa that I am trying to keep CYA free since it is indoors and there is no need for CYA, right?

Well it has been drained twice now. I have the TF test kit and the CYA was over 100 when first drained. After draining it showed 0. About a week later I tested and it showed a CYA of 40 again. I drained it again and tested the refill. It showed 0. Well here we are again a week later and it is up at 30 now!

What gives? I am using BLEACH, MA, Baking Soda, and 20 mule team Borax. It has a cartrigde filter and that was rinsed off the last drain.

So where is the CYA coming from?http://www.troublefreepool.com/posting.php?mode=post&f=10#

 

[JasonLion]

The great majority of the time, CYA comes from a chemical you are adding to the spa. On the other hand, nothing that you mentioned using adds any CYA. Is there any chance that you, or someone else, is adding anything else (like dichlor)?

Another possibility is that your testing is faulty. This isn't likely if you are using a TF100 or Taylor K-2006, but still remotely possible if there was a substantial amount of contamination from somewhere that did have CYA. On the other hand, if you are testing with test strips, invalid test results are quite likely.

It is also possible for CYA to crystalize in the plumbing, and then dissolve back into the water when the CYA level comes down. This is fairly rare, but possible.

If you are using chlorine, then it is a good idea to use a little CYA in a spa, even indoors. Take a look at http://www.troublefreepool.com/how-do-i-use-chlorine-in-my-spa-or-pool-t10095.html.

 

[Guest]

There was a lot of buildup on the old pump that failed. I just thought it was either Chlorine or Calcium, maybe CYA? A cartridge filter would not hold the CYA like DE or sand, right?

They were using TriChlor tabs in the autochlorinator, but it is empty and turned off. The other pool guys who are just supposed to do the cleaning claim they only ever used liquid chlorine.

 

[JasonLion]

Buildup on the outside of the pump would be unrelated. That normally comes from a slow leak. As the water evaporates it leaves behind everything that was dissolved in the water, usually mostly salt and calcium.

CYA can crystalize on the inside of the plumbing when the CYA level is very high. You wouldn't have any way of seeing it and it doesn't matter what kind of filter you have.

 

[Guest]

It turns out the pool service wasn't adding anything, just shock!!!! Dichlor with stabilizer.

Guess you need to ask "what exactly have you been doing" versus "did you add chemicals."

I thought it was a pretty straight forward question.

 

[PaulR]

Like Jason said, a small amount of CYA (20-30) in a spa is still helpful. You aren't protecting the chlorine from sunlight in an indoor (or outdoor covered) spa, but you are taking advantage of the fact that CYA buffers chlorine, making it easier to maintain a reasonable sanitization level.
--paulr