Possible ways to lose CYA?

[bacevedo]

I understand that the normal way for CYA to drop is by splash out, backwashing, etc.

However, my CYA went from around 70, to pretty much zero in the last few months with very little swimming. I don't have any pool leaks that I can detect (i.e. no standing water, salt level rising and not dropping, water bill still the same, etc.)

The last test I did was last year when I filled the pool and it was around 70. I had a pool store test in in August for a warranty claim on my salt cell and they tested CYA at 80 (turned out the cell was just dirty, my bad I thought I had cleaned it recently). I just had the water tested again by them for a warranty claim on the same salt cell (cell didn't seem to be able to make enough chlorine) and they said it was 20. I was like no way, we've barely swam in it. No way I've splashed out that much water since then.

I tested it today and sure enough, I come up with zero on my TFT100 test kit with pretty fresh agents. This makes sense why the salt cell is generating chlorine that's being used up pretty quickly in our intense June AZ sun.

It's possible we have splashed out more water than I expected, but wouldn't that mean we've splashed out 100% of our water over the last year? That seems like a high amount unless we are doing cannonball contests every day for a year.

So, the question is, are there other ways for CYA to drop that don't involve splash out? Is it possible the CYA wasn't being suspended anymore and my new robot that I got last year is vacuuming it out? Highly unlikely, but that's the only thing that's changed on this pool in the last 6 years.

Thanks for any info!

 

[jblizzle]

Yes, if the FC was allowed to go to 0 there is some bacteria that will convert the CYA to ammonia.
Add 10ppm of FC and then retest FC and CC after 15 minutes and report back ... that will allow us to confirm.

Also, you can see a 5-10ppm loss in CYA each month just from getting broken down from intense heat and sun.

 

[bacevedo]

Thank you jblizzle! I didn't realize CYA would break down from intense heat and sun. We get a lot of that here in AZ, as you know! I was under the impression the only way to lose CYA was splash out, so knowing that there are other ways makes me realize I need to test it more often even if we aren't swimming much. I don't think the free chlorine ever got to 0, as my salt cell is generating it most of the day.

I tested my chlorine earlier and I was at 4.5 FC and .5 CC. Yesterday I was at 5 FC and 0 CC. When I tested today, my daughter and her 3 friends had gotten into the pool 30 minutes prior, so I'm sure that's why the CC went up.

I'll add some liquid chlorine now to keep my levels up and then I'm going to backwash my DE filter tonight and add CYA to get back to 70. It takes about 3 bottles and I don't want to add it and then remove some of it backwashing in a month. I don't need to backwash quite yet, but I might as well so I don't waste the conditioner I'm adding now.

 

[jblizzle]

We recommend putting the CYA in a sock and either putting that in the skimmer basket or suspended out in a return jet. That way you know when it is dissolved and it wont just sit in your filter in a low flow environment.

You might have to do it in a few batches unless you have some huge socks

 

[bacevedo]

I'm using liquid conditioner - 3 bottles is what it takes for my pool.

 

[jblizzle]

oh, ok, that is some expensive stuff.
What does PoolMath indicate that each bottle will add to your pool?

 

[bacevedo]

It was $28 a bottle at Ace hardware, and I had $17 in coupons, so it came out to about $23 a bottle. Much easier to add and worth it for me.

Pool math says adding 3 gallons will add CYA of 69. I was basically at 0, so it should get me to where I want. I'll be testing tomorrow once it's had some more time to dissolve and the sun is overhead.

I added a full gallon of chlorine earlier in the evening, backwashed, and added new DE. I checked my chlorine levels and I was at 11. We'll see what they are tomorrow in the morning and the evening. I dialed the salt cell back to 80% and will adjust from there.

Thanks for the help!

 

[jblizzle]

Personally, I would start with two bottles and see where that puts you as you may not have been completely at zero.