Who's CYA and CH to believe

[markmac]

Yesterday I did a water test and had the following results;

FC - 4
CC - 0
TA - 90
PH - 7.6
CH - 350
CYA - 55

I previously posted that I'm having difficulty keeping my PH down, and my FC is burning at 5ppm/day at least. I figured I'd take a sample into the pool store to see what they would read. They provided the following;

TC - 0
TA - 70
PH - 7.6
CH - 250 (100 less than mine)
CYA - 30 (15 less than mine)

Since I've only owned the pool a couple months, I've not had to shock it yet, but one recommendation on why I was burning through FC was a stubborn algae somewhere that is eating it up, so maybe a shock would help. Prior to getting the water tested at the pool shop, I started the shock using the CYA table with a target FC of 22-24. For some reason, whatever I expect my FC to be (based off chlorine % and volume), it is usually twice as much. Anyway, I added enough chlorine that my test shows 26ppm.

Should I believe the pool shop test over mine for CH and CYA? If their CYA is correct, am I to be concerned with a FC in the 20's? Given my rate of FC burn, I'm wondering if their CYA result is better and thus the reason why I go through so much FC.

Water looks fine, and my overnight loss was 2ppm, but the sun was just up when I tested it. I'll double check again tonight to be sure.

 

[Bama Rambler]

What test kit are you using?
If it's one of the recommended kits then I'd believe your own testing.

 

[markmac]

I'm using the K-2006, and the pool shop is using the Leslie's TF100. So basically both are recommended.

 

[Bama Rambler]

Trust your own.

 

[frogabog]

I'm using the K-2006, and the pool shop is using the Leslie's TF100. So basically both are recommended.

The TF100 is from TFTestkits.net

Leslie's doesn't seem to actually sell a FAS-DPD test even though they claim to, and will sell you whatever is on the shelf even if it's not the one you're asking for. If they used no powder, they are using a Taylor 2005 copy in a leslie's box.

If you tested at 26ppm, and they test at 0ppm, it stands to reason that their test was bleached out since you know you had chlorine in it. The DPD (Taylor 2005) test doesn't even test above 5ppm.

CYA is subjective. Two different people might get different results. If they did the tube/black dot test in the store under weird light...??? Well who cares more about the result? You or them? You might even double check yourself a few times just to be sure.