CYA level reduction by accident

[Darth Dad]

Gents,
Have had this pool since 2008. No particular problems. Just found out something interesting.
My CYA was at about 150 at the tail end of last season, and thereabouts after running the pump a bit for opening(getting new reagents now). (Never-to-be-sufficiently-accursed Trichlor pucks before I learned better). Did not drain pool down for the winter (lack of time - I'm on the road a lot).
When I opened my pool, I did my usual routine, which includes dumping in a bottle of "Frog Bam", a copper based algecide (after initial water test). Have not added any metal sequestration products since maybe year #1. Did NOT add much water (maybe 2" - I use a skimmer faceplate plug and bullseye plug for winter). This is a 15' round ABG, 54" wall (6000 gallon). Hayward 3/4 HP power flo matrix. Hayward EC40 DE filter. Clear Solar Cover. Vinyl liner. Del Ozone Big Dipper Ozone generator. Nothing else special. Chemistry not too bad, but I'm going to have to work on my TA (High).
After the SLAM (with appropriate compensation for CYA level), and PH adjust, just to knock down the grungies, the water turned pretty much crystal clear. (2 Days). But I had a considerable amount of purple stuff in a ring around the bottom of the liner.
Did a little investigation and blew the dust off my college chemistry books. I believe it is copper cyanurate. Took a considerable amount (understatement - A LOT)of scrubbing to get it off. Tested water afterward. Now CYA is at 75 (again, my reagents are old. Taylor TF-100). Seems to be borne out by some aquacheck strips I had. And the calculated SLAM chlorination sent my FC WAY over where it was predicted to go, tending to bear out that a good bit of the CYA was eaten up by the copper in the algecide.
Anybody seen this before?
And NO, NO, NO. I'm NOT suggesting doing this on purpose. The beautiful cyan/ amethyst colored salt created is a PAIN to get off the vinyl. Would probably permanently stain plaster or fiberglass.
Ideas?

 

[tim5055]

I believe your lack of CYA and the copper are two different issues. I'll ignore the purple/copper as i agree it is probably copper cyanurate due to your continued use of copper based products.

You say you closed the pool with 150 CYA, but did you test after you opened but before chemical additions? It is not an uncommon happening for folks to open a pool in the spring and find no CYA. CYA can be consumed by bacteria and there is even a new product on the market called BioActive which utilizes the bacteria to reduce CYA levels. Unfortunately the results of testing on this product by members of this forum have not been stellar, but some have shown small reductions and the manufacturer reports reductions in their test pools. I think the science backs up the consumption of CYA by bacteria under the correct conditions. My opinion is that we need to determine the correct conditions for the BioActive to work properly.

I would invite you to do some reading in our Pool School as the products you have been using are really not things we would endorse. Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

So, welcome to TFP!!

 

[Darth Dad]

Yes, did check, and it was still 150.
In any case, it was just an interesting observation/ theory.
Thanks for the information, and I'm still studying/ learning (as most everybody is).
It's amazing how many "professionals" insist that trichlor/ dichlor are the only way to go, without taking into account the buildup of CYA and its attendant problems. In my earlier years, I just believed them. It was only after starting your "pool school" that it all started to make sense.
Thanks again.:bowdown:

 

[JamesW]

The purple was probably copper cyanurate. Anything that precipitates out will remove some of both chemicals. There have been multiple methods for removing chemicals by precipitation. Melamine/cyanuric acic, lanthanum/phosphate, calcium phosphate, iron compounds etc. How much precipitates depends on several factors. In many cases, the process can create more problems than it solves. While some cyanuric acid would be lost to the precipitation, I don't think that it would be much.

In any case, it would not be a worthwhile method to lower cyanuric acid levels.

 

[tim5055]

We all learn every day. I have to ask, how did you get the 150 test, and what was the time period between the 150 test and the 0 test?

As to the "professionals", I think a great number of them are really not trying to mislead. They are just teaching how they learned it.

I invite you to stick around and enjoy the forum!

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