Whom would you trust?

[jeepers]

I am in the process of converting to the BBB and, as recommended here, have been diligently checking and adjusting my chemicals daily. I dropped into a local (and new) pool store yesterday on a whim to check it out and get a water test just to confirm my testing. I did my own test using my Taylor kit just before I left and went in with the following numbers:

FC 4
TC 4
CC 0
pH 7.5
Alk 80
(CYA was 30 a few weeks ago so I expected to be somewhere in the 40s)

Pool store #1 ran my water sample in some fancy tester and reported the following:
FC 3.6
TC 3.6
CC 0
pH 7.9
Alk 90
CYA 55
Phosphates 500

I returned home and again ran my pH on my current and an older Taylor kit and again both showed the same, about 7.5 (very reddish orange, no hint of purple)

Concerned with the validity of the pH results, I took another water sample to Leslie's and they did a drop test and reported the following:

Pool Store #2
FC 3
TC 3
pH 7.6
TA 80
CYA 40
Phosphates 100

I'm confused on whom to believe and how to proceed. I noted to the first pool store that my pH result was widely different and they said that my Taylor kit was shot because I left it in the shed over the winter. Second pool store said that this shouldn't have mattered. It appears that my backup kit confirmed my initial test results which were also also confirmed by Pool Store #2's drop kit.

So, I guess my question here is whether variations like this can be expected between stores and, if so, is one type of store test a better barometer than the other? Like I said, Pool Store #1 used some fancy looking machine and gave me a computer generated printout. Pool store #2 did a drop test and hand wrote the results.

I was prepared to take action to lower the pH and stop using my Trichlor pucks based on the results from #1, but obviously my actions will be different if I trust #2.

Thanks for your thoughts.

Jim

[drband]

Pool store testing is wildly variable because often the tester/associate does not do the test properly. Your test is the one to trust! You are good to go! I would definitely stop the trichlor pucks, though. You should do your own CYA test and see how close you come the the pool store CYA number. CYA testing is very subjective, so if you do your own, exactly the same way each time, you will have a better idea of the level and any increases. Any way, if you are getting in the 40-50 range with CYA, that's plenty for most folks. You don't want to go higher unless there's a reason (extreme heat and direct sun for most of the day, most of the pool season).

Make sure all your levels (TA, pH, CYA, TC, CC) stay in range (BBB method only!) and you'll be fine. Stay away from pool store chemicals.


Good luck.

[PoolDoc]

Actually, Jim, as I looked over those results, my reaction was they were surprisingly close together. I've rarely seen that.

What is very, very difficult for most pool owners . . . and even most in the pool business -- to understand is that
#1 - The 3 result sets you have are within the normal 'range of error' for GOOD pool testing methods, and
#2 - The differences you see are not significant, in terms of pool care.

This variation is why I consider the 'electronic' read outs we see here, for things like FC=3.17 or TA=86, so bogus: the underlying tests used to generate those results can't tell the difference between FC=1 and FC=2 or TA=80 and TA=90 . . . much less the difference between TA=85 and TA=86!

This is also why I dislike the approach inherent in "The PoolCalculator" site, of trying to make a change in one dose: it assumes more accuracy of test results than is reasonable! Except with chlorine doses (where I go over 'overdoses') my preference is ALWAYS to under-dose, retest and then dose again if needed.

Ever since I started PoolSolutions, I've warned people against 'chasing numbers', and if anything, I believe today that that's more important than I do now. In your case, unless your calcium is high, I don't know why you'd need to adjust the pH at either 7.6 OR 7.9 . On the other hand, if it continues to drift up, and you get repeated readings near 8.0, it might be prudent to drop it a little.

But, the bottom line on pools is that IF
+ your pool's chlorine is high enough for your CYA level (see Best Guess) and stable
+ your pH is between 7 and 8;
+ you have some calcium and alkalinity (calcium optional on vinyl pools!);
+ AND your pool is clear, algae-free, and odor-free;
THEN you should leave it alone, except to keep doing what you've been doing!

Two other notes:
#1 - You asked whether you should trust pool store drop tests or pool store machines more: the answer is unequivocal: in general drops are much more trustworthy than machines. Machines have to be calibrated -- and often aren't. Worse, machines are often no more than fancy 'goofy strip' readers, and nothing the machine can do overcomes the intrinsic error in 'goofy strips'.
#2 - Transporting pool samples will USUALLY affect the readings, especially chlorine, pH and TA. For example, if you transported a FULL bottle in #2, but a half empty bottle in #1, the pH difference would be expected, not testing error!

[jeepers]

Thanks, Guys! Glad to hear that it sounds like I'm doing things right. Water is beautiful, I feel like I am understanding the principles of BBB, I'm getting into a testing routine and I've found and identified the Borax, Baking Soda, Soda Ash, 6% hypo, etc so I know exactly where to go and exactly how much it will cost when I need to make adjustments. I finally feel like I am being proactive as opposed to reactive with regard to my pool maintenance.

Ben, I'm glad to hear that your impression is that these tests are reasonably close. I didn't make it clear in my original post, but the biggest effect that these tests had on me was confusion about whether to continue to use my pucks. As you may recall from an earlier post, I had just purchased a 25# tub of pucks before deciding to convert to BBB so I'm trying to recoup as much of that cost as I can. The CYA from pool store #1 was in the 50s, which would make me want to stop pucks immediately. However, the CYA at #2 was only 40 which made me think that I could just continue with the pucks and just bring the pH up bit (expecting it to continue to drop is the pucks in the water).

My compromise: I've left the pucks in the water but closed down the floater a bit. Just going to watch everything else for a few weeks and make minor adjustments, as necessary.

Thanks again for all of your help!

Jim

[PoolDoc]

Personally, I'm drifting, well no, MOVING rapidly toward a high CYA / high Cl approach to pool care. If it were just me, I'd use the trichlor up, use borax to compensate for pH drift, and use the Best Guess tables to adjust chlorine levels as CYA increased.

Oh, and you'll want to keep some chlorine in the pool over the winter, so the CYA doesn't get degraded.

But, this represents a change from my original approach on PoolSolutions, and I haven't worked it out with my moderators and others yet, and there are a bunch of pages to be revised. So, this is "UNOFFICIAL" advice.

[SalemCastles]

Hi Ben,

What are you considering as High CYA? Any concerns over the toxicity of CYA?

[waterbear]

Hi Ben,

What are you considering as High CYA? Any concerns over the toxicity of CYA?

Cyanuric acid is essentially non toxic with and LD50 of 7700 mg/kg in rats. For comparison purposes baking soda (sodium bicarbonate) has an LD50 of 4220 mg/kg, table salt (sodium chloride) has an LD50 of 3000 mg/kg, Aspirin 200 mg/kg, and caffeine 192mg/kg.
This means that baking soda, table salt, Asprirn, and caffeine are progressively more toxic than CYA!