Weird Magnesium Results

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KenRexford

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Using Red Sea, my magnesium was low 8 days ago. So, I followed the BRS calculator with a slightly aggressive guess at water volume and raised up to 1440. That's fine.

Today, having added no magnesium, my test results were 1560, and that's with a hint of purple.

How could magnesium rise on its own? Could dosing alk+calc cause the magnesium to appear higher? Do I suck at running the test kit? Is the test kit nuts?

I let the tank settle after the dosing last week but maybe not enough?
 

Larry L

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Is the test kit nuts?
I assume you're using one of the standard titration-style Magnesium test kits - I don't know the specific numbers for the various brands but I've heard people mention accuracies like +/- 5%. If that's the case and your first measurement was a bit low compared to actual at the time, and your second was a bit high compared to actual at the time, then that would be well within that kind of accuracy range.

I let the tank settle after the dosing last week but maybe not enough?
It's possible things had not reached equilibrium if you didn't wait long enough, it depends a lot on where you dosed and how fast water circulates through your sump/filtration, etc. Although if you dose into the tank in a high flow area and made a reading too soon, then I'd expect the initial reading to be too high, and then get gradually lower as the Magnesium gets more evenly distributed throughout the whole water volume including the sump/filtration.
 

Rybren

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Did you do a water change between tests? Was your salinity the same for both tests? Both could account for some of the change, but testing error still gets my vote as being the most likely culprit.
 
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KenRexford

KenRexford

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Magnesium straight into front of powerhead, so flow mix should be good. Waited a day to test. No water change between tests. I wanted to calculate daily magnesium use.
 
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