Calibration solution for calcium test kits

beachsidereefer · Jun 10, 2016

Hi Randy,

Need your help. I have three different calcium test kits that are giving me very different results. Is there a formula for making a calcium reference solution so I can test each kit against it and figure out which test kit is accurate?

thanks!

Randy Holmes-Farley · Jun 10, 2016

Which kits and how different?

beachsidereefer · Jun 10, 2016

long story short. I used a Hanna tester for about a year and noticed recently some of SPS started to bleach. checked this forum and found that some people were getting inconsistent results so I bought a Salifert kit. When i compared the two the hanna was reading high 300's PPM, the salifert was reading off the charts high 500 plus PPM. Over a period of time I lowered the CA down to where salifert was reading in the 420-430 PPM range, I've noticed the corals appear to be recovering.

This week I purchased a red sea CA kit to compare to the salifert kit. I ran three tests with each kit and both were consistent except the salifert kit was in the 350 PPM range and the red sea 400.

so I have three different CA test kits that all read widely different values. I'm confident that the Hanna is junk because I saw a negative effect on the SPSs. So now I'm thinking either the salifert or red sea is accurate which is why I was thinking a reference solution would allow me to answer this question.

Randy Holmes-Farley · Jun 11, 2016

Many people are not happy with the Hanna calcium tester.

It is not trivial to make a perfect calcium standard at home because of uncertainties of how much moisture is in calcium products, even with careful measurement with a scale. It can be done, but may require baking of the calcium chloride, and even then, a perfect result with just calcium chloride does not ensure a perfect result in seawater.

Reef tanks are not very sensitive to calcium levels, and anything from 380 to 500 ppm will be fine, so I'd just target the middle of that range with the average of the two kits.

beachsidereefer · Jun 13, 2016

Randy Holmes-Farley said:
Many people are not happy with the Hanna calcium tester.

It is not trivial to make a perfect calcium standard at home because of uncertainties of how much moisture is in calcium products, even with careful measurement with a scale. It can be done, but may require baking of the calcium chloride, and even then, a perfect result with just calcium chloride does not ensure a perfect result in seawater.

Reef tanks are not very sensitive to calcium levels, and anything from 380 to 500 ppm will be fine, so I'd just target the middle of that range with the average of the two kits.

thanks as always for your detailed explanations. Do you happen to know if anyone sells a calcium calibration solution you would recommend?

JimWelsh · Jun 13, 2016

The standard I use in my home lab is made up of exactly 1.000g of dried CaCO3 (baked and then cooled in a dessicator) to which just enough HCl is added to dissolve all the CaCO3, and then RO/DI is added in a volumetric flask to make up 1000 mL. The resulting solution has 400.43 mg/L Ca.

beachsidereefer · Jun 13, 2016

JimWelsh said:
The standard I use in my home lab is made up of exactly 1.000g of dried CaCO3 (baked and then cooled in a dessicator) to which just enough HCl is added to dissolve all the CaCO3, and then RO/DI is added in a volumetric flask to make up 1000 mL. The resulting solution has 400.43 mg/L Ca.

Thank you. have you ever tested Salifert and Red Sea test kits against your calibration solution? I'm wondering if you have an opinion on which is more accurate.