Question about RedSea Calcium test kit

[beachsidereefer]

Hi,

when I test for CA using this kit when it gets close to the blue end point the liquid turns purple. Adding another drop or two will then transition it to blue. Once it turns blue, if I swirl/ mix it a bit more and wait another 15-20- seconds it will go back to purple. I'll add another drop and it goes to blue and, swirl a bit more and it will stay longer then the first time but it will go back to purple after abut 30 seconds. Usually the third drop does the trick and it stays blue and does not go back to purple.

My question is which of the three blue transitions is the one I should base my reading on? Historically I base my reading on the final transition to blue where it holds but I was at my local fish shop recently and they thought it was the first. The difference between the first and last is about 20-30 PPM so was wondering what the experts on R2R think!

thanks!
beachsidereefer

 

[jsker]

I wait the the blue

 

[Randy Holmes-Farley Verified Community Expert]

I'd stick to the 5 seconds of mixing they recommend in their directions:

"Add 1 drop of Ca reagent C and shake for 5 seconds. Continue to add Ca reagent C one drop at a time (shake for 5 seconds after each drop) until the color of the sample in the glass vile changes to the corresponding “end” color as shown on the instruction."

 

[beachsidereefer]

thanks all for the replies.

 

[Drauka99]

I use the first change, although I am glad its not just me that was freaked out a little when it changed back after 10-15 seconds

 

[beachsidereefer]

I use the first change, although I am glad its not just me that was freaked out a little when it changed back after 10-15 seconds

right, it's funny how we can over analyze a situation in this hobby and start making mistakes when it's as simple as just follow the directions!

 

[ccajigas07]

Ive been doing it wrong then i guess i do it until it stops turning purple

 

[Randy Holmes-Farley Verified Community Expert]

The slow color change back if you wait too long is, I think, magnesium interfering with the calcium detection.

 

[millsu2]

I know this is an old thread, but every year or so I forget what the answer to this question is and find this thread. I noticed in the Red Sea video that his test never turns purple again, so he must be putting more in until it stops changing back. Also, I found a new video from Red Sea which confirms that you need keep adding until it stops changing back to purple (wait at least 10 seconds):

 

[Dr. Jim]

I found that if it turns back to blue-purple quickly (< 3-4 sec) then it is best to add another drop. It should remain blue for at least 5-10 seconds. Doing it this ways gives me the best match when comparing the same sample to ICP results.