New test kit, CYA question

[frankthailand]

Well i got my two TF test kits with refills a week ago, one was for my neigbour, i just built a pool for him. Very happy with the TF test kit and i have no probs using it easy peasy :-D . Now another mate wants me to test his water, says he gets sore eyes [been using trichlor for years, so it's time for a little BBB lesson] .

Anyway because i am in Thailand it is not easy to get more cya regents. I want to do a complete test for him and see what else is wrong. My question is, with the CYA test can i do the test as normal and if it reads 100. [as i am expecting] Can i then mix the entire solution with an equal amount of water and test again straight away to see if the reading comes down,
thanks in advance Frank

 

[waste]

HI Frank

I believe you can use distilled water to 1/2 the test.

Happy swims for you and your neighbors

If you need more on this, just post.

Take care and I hope your pool is doing well :-D

 

[frankthailand]

Hi waste
That was quick
just to clarify, you reckon if i do the test and it reads 100, then mix the entire solution with the same amount of distilled water straight away and retest, it would still be fairly accurate.

Cheers

 

[chem geek]

That's correct. After you get a reading of >=100, pour that solution back into your bottle where you mixed the original sample with the CYA reagent. Then pour about half out so that it gets down to the halfway line. Then fill up using distilled or filtered water (technically, even tap water should be OK since it won't have CYA in it). Then mix briefly and drop into the measuring tube until the black dot disappears and look again and then double the measurement you read.

[EDIT] I'm not sure why we didn't think of this before, but one doesn't really need to dilute the pool water sample and retest -- one can simply dilute the mixed solution (as described above) since that just cuts in half the amount of melamine-cyanurate that causes the turbidity and is telling you how much CYA is in the water. Thus, saving the CYA reagent is easy to do. [END-EDIT]

Richard

 

[frankthailand]

Thanks guys :-D :-D

 

[Guest]

[EDIT] I'm not sure why we didn't think of this before, but one doesn't really need to dilute the pool water sample and retest -- one can simply dilute the mixed solution (as described above) since that just cuts in half the amount of melamine-cyanurate that causes the turbidity and is telling you how much CYA is in the water. Thus, saving the CYA reagent is easy to do. [END-EDIT]

Richard

Would the precipitate have a greater solubility if water is added?

 

[chem geek]

It's not supposed to. I had asked Taylor about that originally since the official solubility of melamine-cyanurate is equivalent to 20 ppm. They told me that this was only at a pH of 7 whereas at low pH the compound becomes essentially insoluble so Taylor puts a buffered acid in their reagent for that reason. Diluting the already mixed sample will slightly raise the pH, but it shouldn't be enough to significantly affect the solubility. Cutting the hydrogen ion concentration in half would raise the pH by about 0.3, and that would be with an unbuffered solution -- in a buffered solution, the pH would barely budge.

 

[duraleigh]

Hey, guys,

I have been tempted from the beginning to post up about using only 1/2 of the mixture when your expecting a CYA result over 50. My resaon for not doing so is it adds one more technicality for the newbie who has to sift out that info and determine whether or not it applies to him.

As you get used to the kit and, more importantly, understand the parameters you're looking for, it should become more apparent that you can use less reagent......D-a-m-n, I think I just wrecked my refill business!!

 

[Mona]

Ha ha, Dave! You're funny, good way to stick foot in mouth!! But if most people are like me, I'd rather test straight forward without worrying about correct dilution and then doubling numbers. So we'll still need those refills!! :-D

 

[AV8TOR]

[EDIT] I'm not sure why we didn't think of this before, but one doesn't really need to dilute the pool water sample and retest -- one can simply dilute the mixed solution (as described above) since that just cuts in half the amount of melamine-cyanurate that causes the turbidity and is telling you how much CYA is in the water. Thus, saving the CYA reagent is easy to do. [END-EDIT]

Richard

My CYA is 100 or 100+ so are you simply saying use the pool water to the bottom of the label then only fill the R 0013 half way up the line then the rest of the way with distilled or tap water. The indicated value is then doubled?

I am with Mona as I would rather use the test as designed but I am planning on a water change to dilute my CYA and would really like to know just how high it really is (100 or how much more to determine % of water change)

When doing this test I can easily see the changes from clear to cloudy and then slowly watch the black dot disappear but after it would disappear it would gradually re-appear. I kept adding a little more and I repeated this till it did not come back. Is that the correct way or stop after the first time it disappeared? Maybe it had something to do with minor turbulence when adding solution to the vial.

Thanks

 

[chem geek]

The black dot disappearing shouldn't change very much with time. You probably had bubbles in the water obscuring it. Wait a bit for the water to settle and then it should stay fairly consistent. If you wait a very long time, the solution could settle into precipitate, but that probably takes quite a while since I've never noticed it.

As for dilution, you would use the normal amounts for the test with half pool water and half with CYA reagent and mix for 30 seconds. The difference is that instead of using that cloudy solution directly and only seeing that the CYA is 100+ ppm, you pour half of it off and add tap water to fill up the bottle again (i.e. you dilute the cloudy mixture 50/50 with tap water) and mix (briefly; no need for 30 seconds). You then use this diluted mixture in your viewing tube and whatever you measure, you then double that result. So if you end up with 70 ppm, then you had 140 ppm CYA (approximately).

Richard

 

[duraleigh]

When doing this test I can easily see the changes from clear to cloudy and then slowly watch the black dot disappear but after it would disappear it would gradually re-appear.

Wow! That's a heretofore unreported experience. Anyone else seeing these results?

 

[waste]

Dave, I haven't had the need to use my new TF 100 yet (as all the pools are closed), but I have seen the same thing with the Taylor 2005 (and as Richard said, I believe that it was turbulence from the mixing and 'squirting' the solution into the view tube too quickly - I know I posted this possibility on one of these sites, but doubt I could quickly find it ) What I do now is, after shaking the bottle for 30 seconds, let it settle for ~ 5 seconds and then tap the side a few times before dribbling the mix down the side of the view tube -- since I started doing it this way, I no longer get the reappearing dot :idea:

Thanks again for the kit, I can't wait to use it next spring (or maybe an indoor pool will need some testing before then :-D )

 

[AV8TOR]

When doing this test I can easily see the changes from clear to cloudy and then slowly watch the black dot disappear but after it would disappear it would gradually re-appear.

Wow! That's a heretofore unreported experience. Anyone else seeing these results?

Dave to better explain, I am only seeing an ever so faint dot re-appear. It is within 5 seconds or so. Could be bubbles as CG suggests. Pouring in the solution to the view tube could have cause them.

Do you pour constant until it disappears? I poured until it was pretty close to gone then I poured in smaller batches. Next time I will squirt it along the side walls and let it run down that way.

 

[AV8TOR]

As for dilution, you would use the normal amounts for the test with half pool water and half with CYA reagent and mix for 30 seconds. The difference is that instead of using that cloudy solution directly and only seeing that the CYA is 100+ ppm, you pour half of it off and add tap water to fill up the bottle again (i.e. you dilute the cloudy mixture 50/50 with tap water) and mix (briefly; no need for 30 seconds). You then use this diluted mixture in your viewing tube and whatever you measure, you then double that result. So if you end up with 70 ppm, then you had 140 ppm CYA (approximately).

Richard

This is different that you mentioned above with using; half pool water (half way to the bottom label)- have reagent (now level to the label bottom)- then filling the remainder to the top line with distilled water - test and double the result. Just wanting to verify. Actually I can see it done either way with the same results.

 

[chem geek]

Yes, two ways that accomplish the same thing. The first way I mentioned seems harder unless you draw a line on the tube at the 1/4 level. If you do that, then that procedure sounds easier than the second method I described. In fact, in the second method, instead of trying to accurately pour off half which can sometimes be difficult, it's probably easier to transfer the entire amount to another container and then pour back in to the halfway point. Lots of options all accomplishing the same thing!

 

[New2Me]

A small syringe is very good for measuring 5 ml Reagent, 5 ml Sample, and 10 ml diluent(tap or distilled water.) It is handy anytime small repeatable doses ar required. Get them from pharmacy or drugstore, don't need the needles just, the body If you are good with control, you can suck up each amount in a larger syringe, then mix-n dispense from it.

 

[PaulR]

I've read through all this and I'm still a little confused. So the statement is there are
two ways to dilute the test for a wider test range. One is to dilute the pool water
by half, then use the normal test procedure; the other is to use the normal test
procedure, then dilute the resulting mixture by half.
A) pool/tap/reagent proportions of 1:1:2
B) pool/tap/reagent proportions of 1:2:1

I see method A will give correct results, because diluting the sample by half cuts the
actual CYA concentration of the sample by half, and the normal test will give you the
reading for the diluted CYA content. Pretty obvious.

Method B is less obvious, it assumes that diluting the cloudy mixture by half will
have the exact same effect on the reading as method A. Well, diluting the mixture
by half would reduce the concentration of cloudy particles by half; I guess if the
concentration of cloudy particles is linear with the CYA concentration, that would
also give you the correct result.

What makes me nervous is that the scale on the view tube looks logarithmic, and
I'm not sure where that comes into it. The perceived visibility through cloudy
water is nonlinear with the concentration of particles in the water?

(Just got my kit, I suppose I should go try it; my pool CYA should be high enough.)
--paulr

 

[chem geek]

The view tube is logarithmic because, as you say, the perceived visibility is logarithmic. Think of thin sheets with partial transparency, each with the same concentration of CYA. If the first sheet reduces visibility by 20% so that it transmits 80%, then one sheet gives you 80% transmission. Two sheets, or double the concentration, would be 80%*80%=64%. Ten sheets which is 10 times the concentration would be 80%^10 = 11% transmission. Going from a linear concentration to a transmission is, in the limit, an exponential relationship -- going the other way around is logarithmic.

The reason method B works is that, as you said, the amount of light blocking precipitate is proportional to the CYA concentration so diluting before or after doesn't matter. All of the CYA precipitates while there is always excess melamine that is clear.

Richard

 

[PaulR]

Thanks, Richard. I'm a math/software guy, this physical stuff is terra incognita.

> (Just got my kit, I suppose I should go try it; my pool CYA should be high enough.)

Or not. Pool Store Dude (who handled his chemicals like a bartender) reported 60
but I got 30 with the normal procedure, and I had let the sample sit in the house
for an hour to warm up. Oh well.
--paulr