Hanna Checker and ICP Analysis showing massively different readings

Treldeham

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For the last several weeks, my Hanna checker has shown my tank to have roughly 500ppm calcium. I was alarmed by this because I don't dose calcium and have no idea where the extra calcium could come from. I decided to test my water mix (Instant Ocean at 1.024 specific gravity) with an ICP and with the Hanna checker. Also want to note that I only have a FOWLR, so no corals.

The Hanna checker again gave 500ppm calcium, but the ICP analysis said 405ppm calcium. I thought my Hanna checker wasn't working properly, so I ordered the calcium calibration set, but my Hanna checker read that within the correct range (same value, 411ppm, three times in a row), so the Hanna checker itself is working fine. I then diluted a 5ml sample of salt mix with 5ml of RODI, to cut the concentration in half. I tested this with my Hanna checker and it read 412ppm, not 250ppm as you would expected diluting by half.

My only conclusion is that either the ICP analysis is wrong (unlikely), the calibration set it wrong (unlikely), or that the reagents that came with my calcium test are somehow compromised (this is what I'm leaning towards). The rest of my Hanna checkers read everything within expected ranges, so I don't think I'm messing up the process.

Another note is that using Salifert's strontium test kit shows my water mix at 0ppm strontium, yet the ICP analysis shows it at 9.67ppm. However, Salifert's magnesium test agrees with the ICP analysis.
 
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Dan_P

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For the last several weeks, my Hanna checker has shown my tank to have roughly 500ppm calcium. I was alarmed by this because I don't dose calcium and have no idea where the extra calcium could come from. I decided to test my water mix (Instant Ocean at 1.024 specific gravity) with an ICP and with the Hanna checker. Also want to note that I only have a FOWLR, so no corals.

The Hanna checker again gave 500ppm calcium, but the ICP analysis said 405ppm calcium. I thought my Hanna checker wasn't working properly, so I ordered the calcium calibration set, but my Hanna checker read that within the correct range (same value, 411ppm, three times in a row), so the Hanna checker itself is working fine. I then diluted a 5ml sample of salt mix with 5ml of RODI, to cut the concentration in half. I tested this with my Hanna checker and it read 412ppm, not 250ppm as you would expected diluting by half.

My only conclusion is that either the ICP analysis is wrong (unlikely), the calibration set it wrong (unlikely), or that the reagents that came with my calcium test are somehow compromised (this is what I'm leaning towards). The rest of my Hanna checkers read everything within expected ranges, so I don't think I'm messing up the process.

Another note is that using Salifert's strontium test kit shows my water mix at 0ppm strontium, yet the ICP analysis shows it at 9.67ppm. However, Salifert's magnesium test agrees with the ICP analysis.
The freshwater used in the Ca test has to be Ca free. If not, the test will read high. Maybe that’s the issue here.
 

Dan_P

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I used RODI water for it (which was also ICP tested and is free of any calcium).
Your analytical question is whether there is 0 ppm or 1 ppm Ca. ICP results might not be accurate/precise enough to answer your question. Did the ICP results come back with a 95% confidence interval? If not, your question remains unanswered.
 
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