Where did my CYA go?

[Triplejnj]

When I closed my SWG pool last October, my CYA level was between 60-70. I opened it yesterday and began the SLAM process, but my CYA test was not showing any at all! I filled the tube all the way and still clear. There was some rainfall and pumping done occassionally over the winter but I wouldnt expect it to have that big of an impact. How much of a drop is normal and where else could it have gone? I ordered some more CYA reagent in case that is it, but the bottle I have was pretty new, stored in the basement, and expiration date is in 2020.

 

[mknauss]

CYA degradation over winter is quite normal. Couple that with dilution and you get to below 30. Do not add more than 20 ppm worth first as you may overshoot your target.

Also, what does your water look like? Does the pool water hold FC?

 

[DorsalSpine]

Was your water clear when you opened? Was the pool covered? You can get bacteria that eats the CYA and turns it into ammonia. This isn't common but it happens regularly. Don't add more CYA if you have ammonia it will just make it worse. Either use a cheap aquarium test kit for ammonia or do a chlorine test. Add a known amount of chlorine and test for the expected level. Did you get the expected level? Wait 30 - 60 minutes or so and test again. Did you get the same level? The ammonia will "eat" the chlorine quickly. If your pool won't hold FC in the short term you may have ammonia. That's why mknauss asked if it will hold your FC level.

It's probably not ammonia but it doesn't hurt to check. Mknauss knows more about this than I do so follow his advice over mine. I had this post mostly finished when he posted.

 

[Triplejnj]

Thanks for the replies. Pool was green, hence the SLAM. Since I couldn't get a CYA reading I vacuumed, brushed and brought PH to 7.2 and FC to 22 and left filter running overnight. Tested this morning and there was only a 3ppm drop overnight and water is looking a bit better, so doesn't appear to be ammonia. I brought FC back up to 22 before leaving for work. I imagine there will be a bigger drop when I get home as it's pretty sunny out today.

 

[mknauss]

Great. Sorry I missed you started a SLAM.
Get 20 ppm of CYA dissolving using the sock method.

I would not be going to 22 ppm FC without sufficient CYA in your water.

 

[Triplejnj]

Great. Sorry I missed you started a SLAM.
Get 20 ppm of CYA dissolving using the sock method.

I would not be going to 22 ppm FC without sufficient CYA in your water.

Thanks for the advise - I'll be adding 20ppm CYA when I get home later. What is the hurt in bringing up the FC? I was trying get a head start on tackling the algae.

 

[mknauss]

Your liner will not like the high levels of FC without the buffering of the CYA.

 

[duraleigh]

An FC of 22 is wa-a-ay too high without CYA. You should add 30 ppm CYA and then re-start your SLAM.

You are inviting the opportunity to fade your liner by not having CYA in the pool. Done is done and you will probably escape with no harm but the whole reason we publish the FC/CYA chart is to prevent damage to your pool.

 

[Triplejnj]

Thanks guys, duly noted!