CYA testing

[26venus]

I just received my bottle of CYA 50 standard yesterday and I'm wondering how exact is the standard? I know that the CYA test results are probably the most subjective of all results but is the standard exactly 50. The reason I ask is I performed several tests with the 50 std. and consistently read 40.
The tests were performed indoors in a very well lit room under fluorescent bulbs. This is usually the where all my tests are performed.

 

[ship of fools]

I just received my bottle of CYA 50 standard yesterday and I'm wondering how exact is the standard? I know that the CYA test results are probably the most subjective of all results but is the standard exactly 50. The reason I ask is I performed several tests with the 50 std. and consistently read 40.
The tests were performed indoors in a very well lit room under fluorescent bulbs. This is usually the where all my tests are performed.

My guess is the lighting is what is causing the difference .... the directions call for outside in bright sunlight.

 

[26venus]

I considered that but prior to testing the standard I've always achieved the same results outdoors as I have under the lights. I will retest the std. today both indoors and out and post the results.. Thanks to mother nature outdoors was not an option yesterday.

 

[jblizzle]

You certainly do not want light shining down into the tube or you will get a lower reading.

You need to play with the standard to figure out what you need to do get 50ppm ... someone reported then needed to hold the tube up higher than waist level.

 

[26venus]

You need to play with the standard to figure out what you need to do get 50ppm

So what you're saying, as an answer to the direct question, is that I can put faith in the standard as truly being 50. If that's so I can work around whatever it takes to make it read correctly or even compensate if I can't.

 

[jblizzle]

Yes it should be truly 50.

 

[JasonLion]

The standard will be quite close to 50, presumably within +-1, so between 49 and 51, far more precise than you can measure with the test.

 

[26venus]

Thanks guys. I'll still post my findings once I have them.

 

[BillB]

I found out to not be locked in to the waist level test.
Put the standard solution up to the 50 mark in your test vial. Move it up and down under your eyes until the dot just disappears. Notice where the vial is in relation to your torso.
That's where you want to hold it when you test your pool water.
The light doesn't really make any difference as long as you test your pool water in the same lighting.
CYA is an accurate test as long as you follow these guidelines.

 

[26venus]

My guess is the lighting is what is causing the difference .... the directions call for outside in bright sunlight.

Kudos to Ship of Fools! I tried three different areas. Inside, I again got readings of 40. Outside in the shade of my house it read a hair above 40. In direct sunlight, sure enough it read 50. This was repeatable every time. I'm amazed at the difference. Thanks everyone!

 

[26venus]

I found out to not be locked in to the waist level test.
Put the standard solution up to the 50 mark in your test vial. Move it up and down under your eyes until the dot just disappears. Notice where the vial is in relation to your torso.
That's where you want to hold it when you test your pool water.
The light doesn't really make any difference as long as you test your pool water in the same lighting.
CYA is an accurate test as long as you follow these guidelines.

I'm going to play around with this idea. I do all of my testing in my garage which is very well lit. I'd like to keep it that way for a few reasons but mainly because a bright sunny day is never guaranteed. Thanks!