CYA question

[Goolsbymd]

Got my Taylor k2006 kit results will be posted further down but pool store liars said I had 40ppm of CYA. Home tested twice shows 0 so added 4lbs into a sock last night and threw in roughly 40oz of borax to counter the pH drift due to it not being the liquid stabilizer. Well 80% of the CYA is dissolved but my pH is staying steady which is great but I was thinking it would have taken the entire box (74oz) of borax to counter 64oz of stabilizer. So I'm wonder if the drop will happen slowly over time or is it mostly done dropping? CYA has been in front of return jet for 16 hours with pump running entire time.

pH 7.6
FC 7
CC 0
TA 80
Borates 37 (got strips but going off amounts I have put in)
CYA 56 (waiting a week, going off amount added)
Salt 2800

[aylad]

The drop is probably pretty much done. I can't explain the chemistry behind it, but I do know that addition of CYA has very little, if any, effect on your pH. And what little effect you might have seen will be countered by the natural pH rise from a SWCG anyway.

[waterbear]

Any pH change from CYA addition is normally taken care of by the normal buffer effect of the bicarbonate in the water (TA) and by outgassing of CO2 so the addition of an additional alkaline matierial to raise pH is totally unnecessary and often counterproductive to keeping the pH stable.

It sounds like you used the pool calculator's ("effects of adding chemicals" section to figure this out and discovered one of the pitfalls of its use, it does not take into account the effects of buffers in the water and the rate of pH change vs the rate of outgassing of CO2 (which, since CYA is so slow dissolving tend to counteract each other nicely), and so on.

Basically, you are overthinking things and making pool care much more complicated than it really is. Also, with your Goldline SWCg you want to get your CYA up to 80 ppm and 4 lbs in an 8500 gal pool only gets you up to about 50- 60 ppm from 0. Give the CYA a week to dissolve, retest. and then add enough to get it up to 80 ppm, which, if you were truly at 0 ppm when you started, would be about another pound and a half by weight.

[waterbear]

The drop is probably pretty much done. I can't explain the chemistry behind it, but I do know that addition of CYA has very little, if any, effect on your pH. And what little effect you might have seen will be countered by the natural pH rise from a SWCG anyway.

Just to clarify, SWCGs don's cause pH rise, outgassing of CO2 does. SWCGs increase aeration and that increases outgassing.

[Goolsbymd]

I know I need another lb of CYA I just wanted to add 90% see how it effects chemistry then add the last bit so I didn't over shoot. I did use the effects of adding chems to double check things.

[Goolsbymd]

Waiting a week, what is the reason for that? So the CYA goes through the sand, right? I have a cartridge filter so I would imagine once it is dissolved it's all in the pool? Or does CYA have some kind of don't know how else to say it but like a timed release to take effect?

[waterbear]

Waiting a week, what is the reason for that?
CYA can take up to a week to FULLY dissolve. Just a safety precation so you don't overdose.

So the CYA goes through the sand, right? I have a cartridge filter so I would imagine once it is dissolved it's all in the pool?
The undissolved CYA will get caught in the filter, be it sand, cart, or DE and stays there until fully dissolved.

Or does CYA have some kind of don't know how else to say it but like a timed release to take effect?
No, it just gets caught in the filter and slowly dissolves there. Wait a week and retest. It's not rocket science.

Even if you put it in a sock as some do (and IMHO, usually unnecessary, just pour it SLOWLY into the skimmer with the pump running) it will pass though the cloth and some will still end up in the filter and dissolve there. It often is all dissolved in a few days but waiting a week is good insurance against overdosing and needing to drain.

[aylad]

Just to clarify, SWCGs don's cause pH rise, outgassing of CO2 does. SWCGs increase aeration and that increases outgassing.

Yeah, I know, maybe I should've stated it more clearly--just trying to keep things as simple as possible :) :)

Jan