Whom would you trust?

[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!

[SalemCastles]

That's good to know ...I've been called a Rat a few times.

[PoolDoc]

That's good to know ...I've been called a Rat a few times.