Delay in magnesium dosing

AFHokie

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Is there a reason that magnesium increases would be delayed after dosing?

I mixed a fresh batch (1.5 gal) of IO tonight and my Salifert test showed it at about 1230 (consistent with previous batches of same bag).

In order to get it closer to tank values I dosed 7ml of Kent Tech M, shooting for 1310-1320. I verified my math with the reef dosing calculator and it was right on. 1ml/gal increases 18.3ppm.

About 30 minutes after dosing I tested as I assumed 1.5 gallons with a pump running would be plenty. The test came back with no noticeable change.

I tested again 3-4 hours later and it was maybe 10ppm higher. Not enough to say it’s not just test variance.

So, is there a chemical process that takes a while to happen and result in readable changes or was my Tech M not shaken up or some other thing?
 

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I don't think there is any delay unless maybe there was precipitation that occurred which would have used some of it up.
 
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AFHokie

AFHokie

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I don't think there is any delay unless maybe there was precipitation that occurred which would have used some of it up.
I didn’t think there’d be a delay either. I’ll retest again tomorrow since a lot of stuff says wait 24 hours. I assumed that was just for a big tank to ensure complete mixing.

I feel like somewhere I read posts by Randy saying the magnesium wouldn’t precipitate. I think they were similar posts about Mg not increasing despite heavy dosing.
 

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I didn’t think there’d be a delay either. I’ll retest again tomorrow since a lot of stuff says wait 24 hours. I assumed that was just for a big tank to ensure complete mixing.

I feel like somewhere I read posts by Randy saying the magnesium wouldn’t precipitate. I think they were similar posts about Mg not increasing despite heavy dosing.

I can double check the math tomorrow too if you'd like
 
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AFHokie

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I think an 18 ppm change is likely hard to detect accurately with most magnesium kits.
Thanks, Randy!

I agree but it should have been an 85ppm change in total. 7ml in 1.5 gallons.

Even accounting for normal test error, there is a clear jump this morning in test results…..or is there?

With salifert the difference between 1230 and 1300 is only about .05ml. Could there be more test error (drop size, plunger movement, etc) driving that difference? It seems that one drop is around .02ml
 

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