Another yelp for pool chemistry help

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PoolEric

PoolEric

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Jun 21, 2018
40
Arlington, MA
Pool Size
20000
Surface
Plaster
Chlorine
Liquid Chlorine
Hello... I'm new here... and really glad that you're here too... 'cause I could use some help.

Backstory: I bought my house with the pool almost 20 years ago... for many years, maintenance was easy, just adjusting pH, adding chlorine and using chlorine tablets to maintain chlorine.

Then, a few years ago, things got more difficult. This year has proven to be the most difficult of all. For the last few years I had an algae problem, and used a bunch of polyquat, which might be contributing to the problem.

When the pool was opened, I had trouble getting the chlorine level up at all. I remembered I was having similar trouble at the end of last year. So... I did some testing... I now own enough test kits to check for the presence of alien life ;)

Here are the numbers:
pH 7.4
FC 2ppm
CC 0
TA 150
CH 280
CYA too high to test, >100

The water is crystal clear, and has been for a few weeks. But I think I read that does not mean the water is safe to swim in.

So, the obvious first problem is CYA. Having read a lot about pool chemistry, I know enough to be dangerous, and I'm not sure how to proceed.

As soon as I discovered the high CYA I stopped using stabilized chlorine, and started using bleach. I was also able to score some liquid shock (10% sodium hypochlorite) at BJ's, and I've been dumping it in regularly. I can finally get the pool to hold a chlorine level. Last night it was around 8ppm (FC), and this morning down to 2ppm (FC). I also dumped in a gallon of muriatic acid, which brought the TA down a bit, and the pH down from around 7.8 to 7.4.

I know I'm doing some of this out of order, but I'm not around enough during the week to properly monitor the levels.

So... my questions:

  1. Now what? I believe the first thing to do would be to lower the TA... it's high... but is it too high? I'm not sure what the best order to do things is, and some levels seem marginal.
  2. When is it safe to swim? When the chlorine level is high enough? With all the CYA, I believe that requires a high chlorine level. The water is crystal clear, and looks very tempting.
  3. My chlorine options seem to be limited... maybe. I'm pretty sure stabilized chlorine is out. What about calcium hypochlorite? My CH is sort of high-ish... is it too high to use calcium hypochlorite? I think that would require less powder than the gallons of liquid I've been using, and I may already cleared out BJ's supply of 10% chlorine.
  4. I use a solar cover to warm the pool... at what point is it OK to use it? I think I read that under some conditions it's a Bad Idea™ to use a solar cover when the pool chemistry is out of balance.

Sorry to be so verbose, I'm just eager to get the pool in good shape so (1) It will stay in good shape and (2) I can get into it. It's a short pool season here.

Thanks for your help!

-Eric
 
First -- what test kit(s) did you use to get those readings?

Second, your CYA is most likely well above 100. You will need to exchange some water.
If you have the proper test kit, follow Step 8 in Pool School - CYA

It is safe to swim in a pool when FC is above the minimum and at or below the SLAM level based on your CYA. You also need to be able to see the bottom of the deep end.

I would not worry about much until you see how much water needs to be exchanged and that is complete.

Take care.
 
Thanks for your speedy reply!

The pool school CYA page you pointed me to was very helpful! One other tip I found you might want to add is to try to shield the top of the tube from glare... that helped me a lot.

According to using the diluted test, my CYA level is now close to 100... which according to PoolMath means I have to replace 50% of my pool water. My water bill is going to hurt!

In the meantime, just want to make sure that, if my FC level is 11-13ppm (according to PoolMath and my CYA level), it's safe to swim? Does it matter which type of chlorine I use (as long as it's not stabilized?)

Anything else I should keep an eye on while I'm performing Swimming Pool Dialysis? ;)

Thanks again!
 
At that FC you are safe to swim. See [FC/CYA][/FC/CYA]

Liquid chlorine is the best sanitizer to use.

What test kit(s) are you using?
 
Oooops... sorry... I mentioned the test kit when I first was composing my reply, but tfp doesn't seem to get along well with Safari sometimes...

It's the ever popular Taylor K-2006
 
As Marty said, "At that FC you are safe to swim"!!! The chart says just do NOT let it drop blow 8ppm (to keep algae from being able to take hold and be sanitary). At the same time, as long as you are below 39ppm (for that CYA level of 100) your pool is GREAT !!! Just takes more chlorine to maintain.

How are you testing ?

Just saw your update. LIVE by the chart till it's convenient to lower your CYA. Good Luck !!!
 
Once you get the CYA diluted with a partial drain and refill, you'll find things much more easy to manage. I'd shoot for a CYA of 50 and then just keep your FC in the 6-8 range and never let it get below 4.

One thing though, once you get the water exchanged, run an overnight chlorine loss test (OCLT) to verify that nothing is growing in your water. If you don't pass, perform a SLAM to kill off the remaining organics in your water. Once you pass the SLAM, let the FC drift down to normal levels.

Also, stick to liquid chlorine from now on so your CYA doesn't shoot back up to where it was. That's what probably got you in trouble in the first place.
 
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