How to test for CYA less than 30ppm?

[singerteacher]

I would like to accurately test my CYA level using the Taylor 2006, but the CYA reading only starts at 30. I'm currently testing at "somewhere under 30" after refilling my pool (new liner) and adding stabilizer conservatively three times and waiting a week for the results to show. I would much rather add the correct amount of stabilizer than keep guessing at it, especially since I'm going out of town soon and have to leave my pool in the hands of an inexperienced pet-sitter.

So, all you chemists out there, I challenge you:

Can you figure out a way to concentrate the test to get an accurate reading under 30ppm?

Or is it actually impossible?

 

[Donldson]

There is a view tube that measures down to 20 ppm, it is included in the TF-100: TFTestkits.net

That is about as low as any reliable test will give you.

 

[singerteacher]

That's a little better ... but still hoping for more accuracy. What if I added half the normal amount of pool water, and half the normal amount of reagent? Or some other combination?

 

[Donldson]

There is no trick, melamine binds with CYA completely. That's why the test works. Unless you plan to take a sample of pool water and evaporate away half of it leaving double the CYA as initially. That seems like a lot of work when you can just add 20 ppm CYA to the pool and get a reading that will be 50 or less.

 

[singerteacher]

... you can just add 20 ppm CYA to the pool and get a reading that will be 50 or less.

I'm not sure how it's helpful to get a reading that's <50 because that's still not reasonably accurate.

Here's a possible scenario with the "just add 20 ppm CYA" instructions: Someone gets <30 on the test, then adds 20ppm CYA to the pool. They wait a week and still gets a <30 reading. Then they add another 20ppm and at their next test, suddenly their CYA level is upper 40s, which is pretty close to a number that makes some BBB users uncomfortable.

I guess I'm griping about the view tubes, which seem to be geared to people who are not using the BBB method. One of the major tenets of TFP it to be conservative with CYA, lest we need to drain the pool when it gets too high. Wouldn't a more accurate view tube, one that measured down to 0, make sense for BBB users?

Judging by the posts on the subject, a good chunk of TFP members must add CYA regularly, because we have a hard time keeping it in the pool. (Personally, every spring, when I reopen the pool, my CYA is gone. It also seems to diminish after a heavy rain!)

At any rate: I'm thinking that I will try the evaporation idea you had. However, I'm thinking I could speed up the process by boiling the water until I've reduced it by 1/2. Any chemists have thoughts about the boiling of pool water and its effect on CYA?

 

[zea3]

Part of the issue is that the test itself is subjective and has an accuracy of +/- 10 ppm. Your just not going to be abl to test accurately below 30 ppm.

 

[woodyp]

The test is only accurate to within +/-10 ppm anyhow. Boil on if it rocks your socks, but you're in minutia territory for no good reason.

 

[Richard320]

Why wait a week to retest?

There was a lot of discussion and experimentation behind the scenes and you can get a pretty good result within a day after all the stabilizer has dissolved.

Secondly, the exact CYA level is not as important as knowing what it is. If you think you're around 20, add 20 more. It really doesn't matter if you end up at 30 or if you end up at 50 or somewhere in between, so long as you maintain FC for that level.

Have you seen Effects of ADding Chemicals at the bottom of poolmath? Assuming you input the correct pool volume up above and have kept track of how much you've added, it will calculate where you should be.

 

[JoyfulNoise]

The melamine turbidity test can not reliably measure below 30ppm (20ppm is a stretch, even with the TF-100 view tube) because the test relies on the human eye to detect the presence or absence of a dot through a turbid solution. It is inherently inaccurate because human vision has many different aspects to it including your brain which will trick you into thinking that the dot is there when it is not. This is why the test has such a large error (tolerance) - +/- 15ppm.

If you want accurate measurements down to 0ppm, that's simple - Hach sells a digital nephlometer designed to perform the melamine-CYA turbidity test. It measures CYA from 0 to 80ppm with 0.1ppm accuracy. As long as you run the NIST calibration standards before the test, it will be quite accurate. It also costs, with all the reagent packs and standards, about $500.

As others have pointed out, the actual CYA level is somewhat irrelevant as long as you maintain the proper FC/CYA ratio...guess what I keep my CYA at? 90ppm...and that's low for my pool. Do I ever have problems with algae or maintaining a clean and clear swimming pool?? Nope. And that's because I keep the proper amount of FC in my pool. Many pool service companies can maintain pools at CYA levels between 100-150ppm. In fact, there's one company around here that injects chlorine gas into pools and they prefer to have the CYA up above 120ppm so that their high FC levels will hold between visits (every 7 days or so).

So, on the low end, the difference between 30, 40, 50 or 60ppm CYA is inconsequential and any attempt to try to get a super-accurate reading on CYA from the standard Taylor turbidity test is just wasted effort.

 

[domct203]

The melamine turbidity test can not reliably measure below 30ppm (20ppm is a stretch, even with the TF-100 view tube) because the test relies on the human eye to detect the presence or absence of a dot through a turbid solution. It is inherently inaccurate because human vision has many different aspects to it including your brain which will trick you into thinking that the dot is there when it is not. This is why the test has such a large error (tolerance) - +/- 15ppm.

If you want accurate measurements down to 0ppm, that's simple - Hach sells a digital nephlometer designed to perform the melamine-CYA turbidity test. It measures CYA from 0 to 80ppm with 0.1ppm accuracy. As long as you run the NIST calibration standards before the test, it will be quite accurate. It also costs, with all the reagent packs and standards, about $500.

As others have pointed out, the actual CYA level is somewhat irrelevant as long as you maintain the proper FC/CYA ratio...guess what I keep my CYA at? 90ppm...and that's low for my pool. Do I ever have problems with algae or maintaining a clean and clear swimming pool?? Nope. And that's because I keep the proper amount of FC in my pool. Many pool service companies can maintain pools at CYA levels between 100-150ppm. In fact, there's one company around here that injects chlorine gas into pools and they prefer to have the CYA up above 120ppm so that their high FC levels will hold between visits (every 7 days or so).

So, on the low end, the difference between 30, 40, 50 or 60ppm CYA is inconsequential and any attempt to try to get a super-accurate reading on CYA from the standard Taylor turbidity test is just wasted effort.

 

[Swampwoman]

Maybe I missed something here.

When i changed my liner and added fresh water, I used PoolMath to calculate my intended target for cya, added it, read it, and it was spot on.

You've changed your liner AND your water, right? So your CYA started at zero. So you don't need to read sub-30 You just need to calculate how many oz of stabilizer you used.