Ummm, where did my CYA go?

[Gigem]

I started the TFP method last summer, and it has been great. I pretty much left the pool alone for the past few months, and am now starting the process of waking it up for the upcoming year...

When I started TFP, I was fighting high CYA. I dumped a bunch of water out of it and got it down to around 80. That worked fine, and the pool was great all summer long.

I didn't do frequent CYA testing as I figured it wasn't necessary. I wasn't using any stabilized chlorine, and I didn't drain out a bunch of water. Just the normal splash loss. Should be minimal, right? So I assumed the level would stay the same, or close to it...

I did a CYA test today and got less than 30. Took it to the local pool store schmuck, and he got 25.

His expert opinion was that it was lost to "rainwater displacement"... I wasn't buying that.

Of course, his advice was to leave it be, because the CYA would be replaced as I added chlorine tablets. The look on his face when I said I didn't use them, and that I used Clorox instead, was priceless!

Anyway... where did my CYA go?

I guess 25 is too low? Not a salt pool, in Houston, Texas. 18,000 gallons, gets a ton of sun in the summer...

Target level?

Thanks in advance...

 

[Leebo]

He's mostly right. The cya was lowered due to the rain water adding fresh CYA-Free water into your pool. Add to that any water you refilled due to backflushing or splashout and it adds up. A drop like that is very common over the winter months over a 3-4 month time.

As for 25 being low........for now there's a good chance that due to the cooler temps that you'll be just fine with a CYA level around 30ish. Once the temps start to go up, then you'll want to up your CYA level as well to help keep the chlorine in the pool.

What's your normal FC lose per day now?? If it's more than 2-3PPM then you'll want to look at raising it, but if not I'd leave it be.

 

[Richard320]

Do you have an autofill, and have you received a lot of rainfall? It could well be dilution.

A few other ideas: the CYA test reads low if the water is cold. Maybe if you let the sample warm up and try again you will get a higher reading, which means you didn't lose that much. Also, be sure you're in sunlight. Even overcast skies can skew the test.

Some people are fortunate enough to get a certain soil bacteria that converts CYA into ammonia over the winter. What's the FC & CC readings? If it is ammonia, it will take a whole lot of chlorox to eliminate it. Try the search function for ammonia and read up on it.

Whatever the case, you have a perfect excuse to use tablets in a feeder. How you get the chlorine in the pool isn't as important as knowing what else you're adding along with it. Trichlor is acidic, though, which could be good or bad. If you suffer from pH rise and use a lot of acid, it'll be great. If you have low TA and not much pH rise, it'll be a problem.

 

[Gigem]

Thanks guys...

The comment about the test reading low in cold water is interesting... It is cold (for Houston) here today, 30's... it was probably mid 90's last time I tested it...

I think I will start my SLAM now, get it all good and let it heat up some around here...

 

[Isaac-1]

Was the water sample at room (swim) temperature when you tested? the CYA test is known to read low on cold water, also you say you did the test today, I don't know if it is as dreary and gray in Houston as it is here in SW Louisiana today, but if so you also need better lighting conditions to do the CYA test, it is best conducted outside in full sunlight with the sun to your back.

Ike