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You know, this test has me pretty confused, I've gotten quite good at all the others except for this one. There is a point where the black dot almost dissapears, but you can still barely see the outline of it. From there to where it is completely gone is quite a spread, like 20-30ppm. So I'm not sure whether I am at 60-70ppm or more like 30-40ppm, and it makes quite a difference in how much FC I should maintain. How should I judge this test?
Yes, it is quite subjective. I find it helps to place the dot over a light background. When I think the dot's gone, I check the reading, then add some more liquid to see if it "goes away" even more. If it does, I take another reading
This test is very subjective. So much so that I have had to remove the subjectivity as much as possible.
My method is painstaking, literally, but is as follows:
1. Clean the tube that has the spot with bleach before EVERY test.
2. Follow the instructions for adding the sample and CYA. Wait at least a minute before the next part. Shake the mixture thoroughly to get the best reading.
3. Go to a north facing window. Check the point at which the black dot appears or disappears, depending on the equipment and test procedure. Make sure that your fingers are not covering any part of the tube.
4. As soon as the dot appears or disappears, that is your reading. Do not try and find another reading if you don't trust your eyesight. If you don't trust your eyesight, find someone who can. I am not being sarcastic here, just trying to make sure the test is being done correctly.
This test is difficult enough without being consistent, but as Ben says it is the most subjective test you will do in checking for CYA.
Hope this helps.
Pat
Ditto to what PatL34 said!
What do you considered "disappeared"? Is that when it's gone when you casually look at it, or when you really strain to see it? That's the part that always gets me...
So, is this the best the industry can come up with? Surely there are more accurate ways of detecting, and I'm sure there are some people (including me) who might pay more for the test, given that it doesn't have to be done very often. Do the pool pros guess like this?
I am certain the "pool pros" as you call them are nowhere near as thorough as I am. They do not clean the tube with the spot enough times to give any sort accuracy or even consistency. The store where I go to for the occasional water analysis does not clean the tube, even when I ask them to.:mad:
That is why I do it myself.
Pat
The alternative is to use a turbidity meter or colorimeter. some pool stores use them. some use the melamine reagent and the disappering dot. Meters are expensive (good ones in the range of about $600 and up) and do need to be calibarated. If the test is done properly it can be as accurate as a meter (almost). Where I work uses the LaMotte Waterlink Express meter to test (it uses little plastic tubes with a measured amount of reagent in them [Unit Dose Vials] and 3 ml of water is added for the test. They are thrown away, tube and all after each individual test. The meter is calibrated with a blank before each battery of tests) and I get identical results at home with :
1 Ben's ps234s
2 Taylor K-2005
3 Walmart Aqauchem 'cheapie' kit
(as a side note test strips always give me a lower reading)
Another pool store in town uses Taylor's water lab and the cya results depend on who is doing the test. When the owner does it it matches. when the young girl does it it is ususally low (prime example of bad testing procedure, i guess)
The way I do the test at home is as follows:
The first test I do is CYA and I read it about 3-5 minutes after I do it. I start doing other testing in the meantime, usually my FC, TC and maybe pH.
the procedure I use is:
1. make sure the pool water sample is at room temperature (70-80 deg.) before I start because cold temps will slow down the reaction and can give you a low reading because of incomplete precipitation and I have read that high temps (above 80 deg.) can also have adverse effects on the reading (don't exactly know what but possibly allowing some of the precipitate to dissolve and also give a low reading) and then mix pool water sample and reagent in bottle and shake for 30 seconds.
2. let bottle sit for a few minutes and continue with other water testing.
3. make sure I read CYA test before 5 minutes from time of shaking has elapsed. (don't know how important this is but I have read that the test should be completed within 3-5 minutes from different sources)
4. before transferring to CYA tube shake bottle hard for 10-20 seconds.
5 .VERY SLOWLY (almost a drop at a time) transfer solution to tube either with northern window light or outside in shade. Tube is at waist level.
6. read results when black dot seems to completely dissappear.
7. If I want to check my results I pour solution out of tube back into mixing bottle and repeat test. (this is a good way to learn if you are having trouble reading it.
8. wash tube and bottle out carefully and completely so no residue is left in tube
I am the first to admit that I am anal about my water testing!:D but if you are having problems then perhaps you might want to try something similar to this.
Thanks for all the great responses. Ever since deciding to build the pool I've hoped for a digital chemical reader, where I dip it in the water, and it instantly gives me a digital readout of all chem levels, and/or tells me exactly how much of what to add to bring the water into balance. I wonder what such a device would cost or if it's possible to build!
I grew up with my pool owner friends' parents always doing the "strips" or the dropper test, and always felt it very subjective. What if you're color blind, or what if your strips are bad, etc...
The CYA test takes practice to get right. You should try to always do it the same way, everytime.
The nice thing about the test is you can run it several times in a row--just empty the test tube back into the squeeze bottle and do it again. No need to use more reagents!
I hold it at waist level, facing the sun. I add the liquid, slowly (DUH!!!!!) and see when it looks like the dot is disappearing. I move the tube back and forth a little to see if I can see the dot, and add more from the squeeze bottle until I cannot.
Then remember that if you are NOT on a line, the scale is logarythmic, not even. So halfway between 30 and 40 is NOT 35, but more like 33, and 3/4 of the way to 40 is more like 35.
Again, though, do it the same way everytime.
As the title of Ben's "best guess" chart implies, this isn't an exact science so there wouldn't be much point in worrying about perfection with this test.
So far, I've been able to get consistent readings as long as I test in similar light conditions. If I run into algae problems, I'll run the chloring levels a bit higher. No biggie. ;)
This is the question I still wonder about. Which of the following have "just disappeared"? (Click on the photo to get a larger copy.}Quote:
Originally Posted by vanhout
http://static.flickr.com/68/154212577_da48eec6bd_o.jpg
Empty, 50, 40, 30, 20
What do you think?
cheers,
Scott
(I'll leave the picture up as reference if we come to consensus.}
My $.02 is that it doesn't disappear until the last (20ppm) shot.
Probably somewhere between 20 and 25, and that's probably as accurate as you need to be to know where you stand
I would have said "keep going, I can still see outline of the dot"
Excellent pictures by the way!
MikeK
Cool pictures.. I thnk I'll post them next time I have to "make the call".
Someone said I can dump my test water back into the squeeze bottle and re-use it???? So I *never ever* have to buy reagent ever again?
cygnusecks - I believe they meant that they can use the same sample to take another look at the results in case of doubt. You have to do it all over again for the other tests, but this test you can just add the same sample back into the tube to see if your eyes see the same thing.
My question always has been - how high is waist high? I'd rather Ben put a number like 2 feet, 18 inches, etc. on the instructions. I'm over 6', but someone else may be 4'6" and have shorter to their waist.
Glad to read that it is as subjective as I thought.
Regarding the pics above I would say it is in the neighborhood of 20 ppm and that is close enough for government work! It I got that reading I would bump up the CYA bit until it read around 30 or 40 ppm.
As far as how high is waist high? The important point is that the tube is not 6 inches below you eyes but at about a level of your upper arms straight down and your forarm at 90 deg. to them, which for most people would put your hand holding the tube somewhere around your navel. It's not rocket science! You just don't want to be peering right into the top of the tube like it was a microscope. Holding the tube 10 inches higher or lower than someone else is not going to change the reading by any significant amouht!
Hope this helps.
The HAVE devices like that...they are called digital pH meters, ORP meters, Colorimeters, turbudity meters, and conductivity meters (and possibly some others). Good ones can set you back thousands of dollars. The also require standard solutions to calibrate them and some of the electrodes needs special care such as being stored wet. They are actually more work and more time consuming in the long run and won't really give you much benifit over a drop test. You don't NEED that level of accuracy to maintain your pool!Quote:
Originally Posted by cygnusecks
Reagents do go bad, Strips have very little precision, but electrodes go bad and batteries get weak also and if a meter is not properly calibrated (pH meters are a horror to calibrate!) then the test results won't even be as accurate as a strip! I have worked with several of these types of electronic testers over the years in laboratory settings, as an aqaurist, and as a 'pool store guy'. I use a drop based kit for my own pool and my water is perfect.
Those pictures are great! But only as an example. I would NEVER estimate the CYA level based on them. Cameras pick up things the eye doesn't and may be making the CYA look lower than it is.
I have outdoor speakers on my deck. No matter HOW I look at them I cannot see the woofer and tweeter through the grill. But the pictures taken CLEARLY show them... That's an example of my point. The camera is a better "eye" than the eye.
I was with MikeK; when I took the pics I thought it might be lower than 20. But that's probably interpreting "the center is no longer darker than the outside" rather than the black dot "just disappear".
Interestingly (well, for photo geeks), these pictures overestimate the actual readings due to a combination of two factors: (a) they were taken very close to the top of the vial rather than from a distance (i.e., not waist high), (b) the small depth of field of cameras in general, but particularly at this small distance, causes the cloudiness to have a greater effect in the picture than in person. Indeed, although I can hardly see any variation in brightness in the 20 ppm picture, I could see definite variation in person.
Scott
Well, one thing that helped my original predicament. There wasn't much difference in appearance of the dot from 80ppm to 50ppm. So what I did was to test a new sample made up of 50% pool water and 50% tap water to dilute the sample and see how it went. Well this time it was much easier to read and the result seemed pretty conclusive at 40ppm (which unfortuneatly means that I am at 80ppm, too high). Anyway perhaps higher CYA numbers are harder to read than lower?