Where did my CYA go?

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K

kj5kb

0
Aug 8, 2010
100
SW of Kansas City
Moved to Kansas last year and got my first in-ground pool. Once opened this Spring I did a full battery of tests and CYA was ~40.

My previous experience is 3.5 years with an 8000 gallon vinyl AGP, using BBB method with occasional dichlor. Pool was generally stable once opened each Spring, and I rarely performed the full battery of tests except for PH and chlorine weekly. I normally kept CYA at 40-60...if anything it went UP over the season.

Back to the 'new' pool- I've noticed I've been using a LOT of chlorine lately, and over the past two weeks the pool has been used daily. I realized I haven't run a complete panel of tests in a couple months and haven't checked PH in a couple weeks. I've been using mainly 10% liquid CL, some Cal-hypo and occasional trichlor puck.

So...today we have (K2006 test kit)

FC/CC 0
PH 8.0+ tested twice
TA 90
CH 150
CYA 0 ???? tested twice, second time with new reagent
Temp 80F

My understanding is that CYA doesn't just "go away". I would expect to lose a little with backflushing the sand filter, but zero? Could the test be incorrect due to high PH? The pool water + reagent was CLEAR.

I realize the main problem is I've been lazy with my water testing and just dumping Chlorine in. Need to check CYA as well as PH and chlorine at least weekly.

I was estimating my pool at 18000 gallons. Recalculating today it's probably closer to 20000, possibly more, I'm not sure exactly "how deep the deep end is"... So I may have been underdosing chlorine.

I added 23oz of muratic acid to bring the PH down, and 1 gallon of 10% CL and 2 lbs of cal-hypo (was out of liquid). Also put 3 trichlor pucks in the floater.

Picked up more liquid as well as CYA today and will reassess in the morning. Working till 11PM so not much more will get done tonight. May add a partial dose of CYA when I get home.
 
PH does not impact the CYA test. It is possible if FC is allowed to drop close to 0 or all the way to 0 then bacteria can grow and consume the CYA. It seems to be more prevalent this year.
 
That would 'splain it. FC dropped a few times when we weren't paying attention, plus I was overconfident due to my previous experience and wasn't checking PH and CYA often enough. This pool gets full KS sun vs my previous one with partial Northern Ohio sun, so I figured the sun was just burning off the Chlorine faster!

Got 4 lbs of CYA, now realize I should have got at least 8. Will add the 4 to the skimmer and get more tomorrow...
 
That's one thing I do miss about my old cartridge filter. Pour it slowly down the skimmer and forget it. Probably get lost in never-never-land if I did that in a sand filter and then flushed out.

I have plenty of nylons I can use - I use them for filters in my aquaria.
 
So 14 hours later...

PH 7.5

FC <0.5, (but not zero) wasted a lot of $$ on adding chlorine during the daytime...hope it did SOME good!

Added 2 gallons of 10% bleach.

Put 4 lbs of CYA in a nylon stocking...filled stocking over the pool next to a return, all the dust went in the pool :)
Now coiled up in skimmer.

Got HTH 96% CYA at Ace in Olathe KS today for $17.99. Thought that was a bit much til I remembered it ain't cheap....and it was available right when/where I needed it!

HTH 10% liquid Chlorine is $4.99/gal @ Ace. Independent Pool store doesn't stock ANY liquid chlorine (tho they have darn near everything else at reasonable prices!). Walmart here doesn't seem to stock stronger than laundry bleach.
 
So as of 10PM last night, ~48 hrs after adding the first of the CYA, my CYA 40, PH 7.2 (easily fixed) and FC at 5.5 (I added some Monday and Tues). Water is crystal clear...didn't realize how cloudy it was before! Added a gallon of 10% bleach to bump it up to shock level. Should be good to go from here, just need to SLAM and pass an OCLT.

Now that I know CYA CAN be consumed I will watch it more closely. Bought a pint of reagent so I'm set.

Thanks for the advice! Don

<so the rest of this is just unrelated ramblings>

Compared to pool store CYA I've used in the past, the HTH CYA was finer grained and dissolved much more quickly. I expect my CYA to go up a bit over the next few days, but shouldn't go over 60.

Now that it's clear I see lots of debris in the deep end, either organics or sand, not decided yet. Read several threads on those so that should be easy to figure out. If sand, my sand filter is due for a sand change, and possibly a replacement filter anyway due to age. The drain threads are just about stripped and the cap barely holds on, + the valve does not operate smoothly. I can get a whole new filter for about $250 + sand.

Will have a harder look round at all 3 local Walmarts, maybe one has the 8.25% bleach at a reasonable price...or even pool bleach if I'm lucky. Last time I looked it was 6% and the price wasnt worth the bother of hauling many single bottles thru wal-mart then transporting home - vs cases of 4 10% HTH liquid at Ace which I can load 4 (16 bottles) in a cart and sit nicely in the back of the truck (they don't even slide around on my plastic bedliner).
 

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