High CYA Level after one year with new water

[dandjpool]

Our vinyl liner was just replaced last year in April and the CYA level is off the charts already. It measured at approx 120-130ppm.
How is this possible? I haven't added any stabilizer or other chemical that might raise it. Just bleach, soda ash (almost 30lbs to get pH right), clarifier and the dichlor that gets fed.

The only negative in my setup is a dichlor feeder and it's been feeding like crazy over the past week. Sucked up about 20lbs in 10 days.
I shocked with bleach thinking it just needed to be shocked and the chlorine level barely budged. I didn't think it could possibly be the CYA level but finally tested it yesterday.

Here's the setup: The feeder (Polaris Watermatic) is setup to pull through the drain plug in the filter pump and it gets fed right after the heater. So the chlorinated water is pushed through the filter then the heater before entering the pool. I am thinking this might be bad.
It has a water flow in the bottom compartment that allows the powder to dissolve before being fed. The chlorine level is tested by ORP.

I know dichlor adds CYA but this much in a years time? Could it be low-grade dichlor? I got it from Leslie's Pool.
Last time I had this high a reading it was after 5 years and I added stabilizer because I didn't know any better (pre-tfp).

Thanks

 

[Smykowski]

How big is your pool?

What kind of water replacement do you get over the course of a year (backwash, splash out, etc.)?

Did you use dichlor last year after the liner replacement?

 

[dandjpool]

Pool is approx 20K Gallons.

I drain below returns when closing and fill above. I have a cartridge filter, so no backwash. I probably had to add 1K gallons every 2 weeks for splash-out/evaporation.

Yes, dichlor is the main chlorine used in the pool. I use bleach to shock.

A couple things I forgot to mention: I opened the pool March 15th this year because of the warm weather (I'm in Illinois) so the heater has been running a lot at night to keep the pool at 83 degrees.
Also, the auto-cover is closed whenever we are not in the pool. I've noticed that this messes with the pH a little for some reason, I think. When it's open more regularly in the summer and when I intentionally leave it open for the day to let it "breathe" there are less issues with pH.

 

[Smykowski]

Sounds to me like a CYA reading that high is not unreasonable.

According to the pool calculator, 20lbs. of dichlor in a 20K gal pool will raise CYA by 60ppm. Add to that the CYA in the pool when you closed in the fall (again, using dichlor all summer, closing at 60-80ppm is certainly plausible), and 120-130ppm is well within the realm of possibility.

Since dichlor lowers pH, this also explains the high demand for soda ash.

 

[duraleigh]

Di-chlor is the source of your CYA. Based on what you tell us, you have no other source so, yes, that is what has gotten it that high.

For every 10 parts chlorine you put in your pool, you add 7 parts CYA if you use di-chlor.

I have NEVER liked di-chlor mostly for that reason. It's just too easy to let the CYA get away from you.

Your only practical recourse is to do a partial drain and refill to get your CYA down to a manageable 50ppm.

The percentage of CYA should be right on the container and I think they pretty much only make one grade but I am not competely certain.

 

[dandjpool]

I will start the drain tonight. Last time I had to do 50% then 50% again to get it right. My water bills will suck.

The feeder has tags all over it that say "Dichlor Only". Why would that be? I would prefer to use the calcium hypo. Would it screw something up?

Could the way the dichlor is being fed have an impact on the efficiency? It gets fed/pulled before the heater then warm water is returned/pushed back into the feeder (water that has just been chlorinated) after the heater. I noticed it feeds a lot more often when the heater is running regularly.

Thanks again for your answers!

 

[duraleigh]

I would prefer to use the calcium hypo. Would it screw something up?

That's not a very good plan, either, in that Cal hypo adds unwanted calcium to your water and you must drain to get rid of it, too.

I can't help with info on the dichlor feeder but I would encourage you to switch to bleach. It is cumbersome but it puts NOTHING in your water that will cause you any bad side effects.

If you don't want to give up the automation, there are some available options to feed bleach automatically.

 

[dandjpool]

I just realized who you are. Best test kits ever! I need to get another one. I'll be ordering soon.

I will look into the bleach feeder. I've seen it on here in a few different places. The only thing I like about the current feeder is that I'm away from home quite a bit and it's nice to (at least believe) the chlorine level is being kept up. From what I understand, the bleach feeder is set by drip rate and needs a bit of tweeking.
I thought calcium wasn't much of a concern with a vinyl lined pool.

 

[duraleigh]

I thought calcium wasn't much of a concern with a vinyl lined pool.

Too low is not a problem, but too high calcium causes all sorts of issues in any kind of pool and needs to be avoided.

Since you are aware of the effect of dichlor, you can still use that feeder but would have to test CYA often and drain off and refill some water when your CYA got up around 60ppm.

(Thank you for your nice words about the kit :lol: )