CYA water to reagent ratios

[H2O_Keeper]

Just got my testkit and was wondering about accuracy needed using the bottom of the label and top of the label as the guides for how much water and reagent. The reagent will be consistent due to the label heigth but it appears my label is like 1/8" inch low from making a 50/50 ratio for the test.

I havent yet went to the store to get a syringe to find off how many ml difference there is. Is it that critical for this test if the ratios of water to CYA could be off as much as 10%? I have a 100+ CYA and since I have dilution on top of the first mix I dont know if I would be signifcantly introducing a margin of error starting out.

Long story to ask how critical is a 50/50 mix for this process?

 

[JasonLion]

The error when reading the test is around +-20 units. For a reading around 100, that is +-20%. A 10% error in mixing would reduce the accuracy further, but not in a way that really matters. Of course an 1/8th of an inch in the bottle might be more than a 10% error.

My label was tilted, so I re-calibrated the label using measured portions of water and a waterproof marker, which was simple enough. Even if your label is fairly far off it isn't a major problem. It is more important that you get constant readings from test to test than absolute accuracy. Consistency allows you to make fine adjustments relative to your previous experience, which is what is the most important thing.

 

[H2O_Keeper]

Well I am within spec 15ml to the bottom and 17.5ml width of the label. No problems with the ratios and my label was on nice and straight.

As an FYI I did try and see how what the minimum reagent required for a 50/50 mix and enough to get at least to the 20 CYA level (as high as graduations go on my sight tube). That works out to be 14 ml of reagent. If a person wanted to be frugal you could mark the mix bottle at 14ml and 28ml and use that as your guide. Would mean after every 6th test you would get one for free ... In my case I will probably add the CYA reagent first (15ml) and get close to the top of the label with pool water. Sorry Dave, may of just reduced your CYA refill biz!