For the Chemists

[Mules1]

In my quest to have accurate and repeatable Ca test results (currently I am using Hanna checker - with added pipettes for volume accuracy) but still have trouble with repeatability (convinced it is from the extremely small sample volume) - I have available to me the following test:

This test for relies on titration with ethylene diamine tetra acetic
acid (EDTA), a chelating agent. When all calcium and magnesium ions are
complexed, the excess EDTA reacts with an indicator to give you a blue
colour endpoint
Reagents
Hardness reagent .01M ETDA R-0618
Hardness buffer R-0619
hardness indicating powder R-0620
Apparatus
Burette assembly, 10ml
graduated sample tube, 25 ml
glass erlenmeyer flask, 125 ml
Procedure
measure 25 ml of water in sample tube, add to erlenmeyer
add 5 drops R-0619 buffer, swirl to mix
add one dipper R-0620 powder, swirl
titrate with R-0618 until blue colour end point
Multiply burette reading by 40 to get hardness in ppm


Is this useful?

(As I believe it tests for the sum of calcium AND magnesium ions expressed in ppm calcium carbonate.)

 

[KCombs]

what exactly are you asking? (just slightly confused)

PS....that Hanna checker is junk, I'll save you the time

 

[Mules1]

I am asking if this is a proper aquarium Ca test and is usable.


(and if Hanna is junk - what do you recommend?)

 

[csauer52]

Just out of curiosity, why are so so worried about Ca and not the other pharna as well? TBH, my focus us on alk more than anything else. I find everything else falls into place even alk is correct and stable.

I use Salifert test kits for everything except PO4 for which I purchased a Hanna checker.

 

[csauer52]

Just out of curiosity, why are so so worried about Ca and not the other parms as well? TBH, my focus is on alk more than anything else. I find everything else falls into place when alk is correct and stable.

I use Salifert test kits for everything except PO4 for which I purchased a Hanna checker.

 

[Mules1]

I am technically not worried so much about Ca. I know there is a balance, but that is why it irks me not to have consistent results from my calcium tests. Alk is an easy test with repeatable results - that is generally what I go by.

 

[tecapparatus]

Check out methods of seawater analysis, 3rd ed. It has all these methods, although you'll need a little more equipment that you listed.

 

[Mules1]

I will research. Thank you for the reply.

 

[bertoni]

That sounds like a general hardness test, and it's not very useful in saltwater, due to the high magnesium and calcium content of the water. It's basically testing the sum of the two parameters, which isn't all that interesting.

 

[Mules1]

Yes, it is a general hardness test.

Thank you.

 

[Mekanic]

FWIW I find the Red Sea Pro test to be pretty repeatable despite the small sample size.

 

[Ron Reefman]

I use the Salifert and API calcium test kits and find that they are quite repeatable and always seem to come out with the API kit reading about 20-30ppm lower than the Salifert kit. So I use an average. I guess I don't understand why you are concerned about repeatability? How far off are you when you do back to back tests?