Expected CYA number to jump to 30-40, nothing

[simland]

I want to mark this thread as I'm having a similar issue. I've been trying to get my levels corrected over the past week so I can fire up my newly installed SWG. I added 4lbs of granular stabilizer (HTH walmart) last week expected CYA number to jump to 30-40. I tested when I got back this week (work out of state during the week) and nothing.

I don't want to hijack your thread, I just feel like we are in the same boat. I have no idea where all the CYA went and why 4lbs didn't move it. We've dumped about 1500oz of chlorox bleach along with 3lbs of Cal Hypo Super Shock over the past 2 weeks. The water is crystal clear, but sometimes there is what appears to be dead mustard algae on the bottom. (Hence the constant shocking.) I'm not home enough to properly do it as I've read on the forums. I have to resort to lots of chlorine and hope it survives the week.

I hope we can figure out our CYA issue. There isn't a possibility of getting a false negative is there?

My numbers from Taylor Test Kit read:

CYA: 0-20 (can see dot at full but some cloudiness)
FC: 2.6
CC: 0.6
pH: 7.1
TA: 90
CH: 140
Salt: 3500

 

[JasonLion]

Welcome to TFP!

Are you sure you are adding 90+% cyanuric acid? I have seen 50% sold some places, and occasionally people mix up some other chemical with cyanuric acid.

How large is your pool?

 

[simland]

I have an estimated 25000 gallon pool. It's a simple rounded corner rectangular pool with a deep end. Vinyl. Minnesota. Brand new filters in a Hayward Cartridge Filter. Brand new main pump as the pump motor burned out.

I added HTH Stabilizer which lists at 96% CYA. (I can not find CYA in any other form other than Walmart. I don't want to go to the pool store as they are expensive!)

It has been a week and a day since I added it. Tested with a brand new bottle of reagent. (2 Smaller bottles get used up so fast.)

Thanks ahead of time for help on my issue and thanks for the help on many other's issues. This site/forum is amazing.

 

[JasonLion]

In 25,000 gallons, I would only expect 4 lbs of CYA to raise the CYA level by 19. Assuming CYA started at zero, it is hardly surprising that level tested as zero. Even if it was 100% CYA and it all dissolved, levels as high as 20 can measure as zero.

With CYA around 20, losing chlorine to sunlight very quickly is to be expected.

I recommend you add another 4 lbs of CYA.

 

[simland]

So, this pool (and the water) is not new. We had used the pucks as a way to provide some kind of chlorine to the pool when I'm out of town. (Even this year) There are at least 4-8 completely dissolved pucks worth of CYA in the pool as of the spring opening.

I would have thought the CYA levels would be higher.

The tests don't lie however, so I'll add the CYA.

Thanks for the advice!

I'll follow up in a week on the CYA level. In the meantime, I'm home next week so I should hopefully be able to fight the good fight on the chlorine front as I just got power out to the SWG and turned it on for the first time. Now for bleach...

 

[simland]

1 Week after 4 lbs of HTH Stabilizer (96% CYA):

FC 15
CC .5
pH 7.5
TA 100
CH 185
CYA 30

We had a lot of people in the pool yesterday so these numbers were in a freshly uncovered pool after an evening boost with the SWG. By boost, I mean ran at 30%. (Still trying to dial in the correct % on the Autopilot but normal is around 15-20%)

I went out to Wally World to get some more stabilizer. I can tell it's working as the test is now at least cloudy and obscures the black dot at 30ish levels. I know I want my CYA higher to help with the SWG so I went ahead and put another 4lbs in. I have another 4lbs waiting in the wings for when this 4lbs doesn't raise it enough.

One of the benefits is that this will drop my pH which has crept up a bit, supposedly because SWG do this?

 

[duraleigh]

One of the benefits is that this will drop my pH which has crept up a bit, supposedly because SWG do this?

It won't help it much. Rising pH is a fact of life in SWG pools especially and to many manually chlorinated pools. You can look at the bottom of the poolcalculator to see how much the CYA will change your pH but it is temporary.

 

[simland]

Agreed, based on what I can tell it's likely due to aeration that happens as a byproduct of the SWG chemical process.

As my TA is a bit on the higher end, this should help to bring that down as well. (7.5 with 4lbs of CYA results in about 7.15 pH I believe)

Now I just need to find Muriatic Acid at the local hardware store and I'll be set!

 

[linen]

Hey simland, I noticed you are a fellow Minnestotan

If there is a fleetfarm near you, they have been selling 1 gallon 31.45% MA all summer for 4 bucks (at least the one up in Blaine is).

 

[simland]

Thanks Linen, I'm on the east side, but we have a Fleet Farm near 36 and 694. My local Home Depot says they have 5 boxes in store somewhere. (I have failed to find it each time I've been there for other things, but I've yet to ask.)

My CYA rose to around 45 after putting another 4lbs. I'm guessing the PoolCalculator assumes 100% purity so 45 isn't really off if I did have 0 and have now put 8lbs into the pool. I'm going to have to add more based on the target numbers for SWG.

Reading this time, I don't know how the pH rose without the TA dropping. I believe it was covered the whole week. I understand that this can prevent gasses from escaping?

FC - 19 (Still so freaking high, have not figured out a good setting for the SWG)
CC - < 0.5
pH - 7.4
TA - 100
CYA - 45
Salt - 3400
Temp - 94 Degrees

 

[linen]

Thanks Linen, I'm on the east side, but we have a Fleet Farm near 36 and 694.

I know it well...I grew up in No. St. Paul.

Reading this time, I don't know how the pH rose without the TA dropping. I believe it was covered the whole week. I understand that this can prevent gasses from escaping?

It is the act of lowering ph that also lowers TA, natural ph rise will do nothing to TA. TA shouldn't move much other times (unless you are adding water with a significantly different TA then the pool water).