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Jimbo662

Mag test readings

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My bigger point here is having to add ~10x Mg vs Alk/Ca and not seeing a significant rise in readings.  If the Mg WAS NOT getting used up in the process, shouldn't the reading be HIGHER? 

Typically test 10a-12n, depending on when I have a bit of a break from work.  Usually dose Mg manually directly after testing, Alk & Ca are dosed at nighttime on timers  - I only have a timer w/ minute options, so I am constantly having to switch from 2>3>2>1>3 to try and keep things stable.  Also had a couple runs where I was doing weekly water changes, so that was another challenge in terms of stability.

Ca
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Alk

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Mg - ca - alk - salinity has some interactions.  Mag should be 3ish times ca.  Mag vs ca also buffer alk.   Systems with low mg ca relation can be subseptible to greater alk swings.  If you alk and ca are the same then your mag should be the same and I would defer to the test kit being slightly off.  My main question is why does it matter except from a testing standpoint.  If my mag is anywhere between 1350 and 1600 I'm happy.  If my ca is anywhere from 375 to 500 I'm happy. Ideally I shoot for 450 ca and 1400 mg  If the ratio is off I get very slightly concerned and my do a water change (10%) to help restore the ionic balance but I will normally take no other action.  And usually it's if my mag is like 1700 and my ca is 350.  It's only happened 2 times due to hand dosing and fuzzy math.  Most fresh saltwater in my experience is good on ca and lower on mg then I would like.  The biggest question is Why stress over it?

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I suppose it's mostly from a math/chemistry position, not necessarily a reefing issue.  It's confusing and I'm trying to understand the why.

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From a math/chemisty position the only thing I would concern myself with is, is the mag in acceptable range? Is it in the correct ratio to calcium?

from a reefing standpoint the only thing I would concern myself with is, all the math chemisty questions, am I observing a rise or fall within the same test kit chemicals.  

When you switch test kits you will get different readings.  It happens all the time to me with Hanna alk when I go to a new reagent bottle.  I have seen a difference of 0.5 dkh.  It can be slightly concerning if your not ready for it.  I only care about the rise or fall not the actual number so much as long as it's kinda where I want it.  When you switch to new test kits you should always take back to back readings to see what the new test kit says vs the old test kit.

the WHY is it different.  We pay very little for our test kits and use them over a long period of time.  The reagents aren't lab grade.  Any evaporation out of the bottles can skew the readings.  The manufacturing of the reagent chemicals over a 6 month period can very a little.  When you use drops a little inconsistency in the mix can make it read different.  The relationship to salinity alkalinity and calcium and how they buffer and interact can give a little different reading.  If your not using exactly 2ml and use 2.2 the test can read off.

when I look at your graph I see instability on your alk.  With alk not stable I suspect that you maybe experiencing percipitation.  If you turn your dosers off do you experience a fall?  It appears every time you run your ca up your alk falls.  That is indicative of percipitation as the ca binds the alk.  In these instances I suspect your mag was lower then 1150 and thus unable to bind with the alk before the ca.

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Alk and Ca are dosed 3 hours apart, so precipitation is not likely.

Haven't changed testers at all - Hanna for Alk, Salifert for Ca & Mg.  Definitely not using them for a long time, as I'm testing almost every day.  I'm fairly obsessive w/ getting the correct measurements on all as well - .2ml off?  lol!  I will re-scoop the granular reagent 5x if I think it's anything but flat on the scoop!  I'll also re-do the test if I feel I've messed anything up, or if I get any kind of wonky result.

The rise and fall has to do w/ the fact that I have to manually adjust the time on the dosers and I can't go smaller than minutes.  I simply don't have the ability to dial them in any better than I am today.

What I'm hearing (reading) is that I need to worry about the Alk level, but not so much the Ca and Mg, so long as they aren't crazy.

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Right, stable alkalinity is more important than calcium and magnesium as it's what corals use to build their skeletons and it's being used by all algae in a system so there's a much heavier demand for it.  Calcium and magnesium need to be kept above certain numbers (I use 360 mg/l calcium and 1200 mg/l magnesium as minimums).  This discussion does highlight the issue with inacurate or aging test kits and I replace my test kits at least yearly and always compare the new and old test kits to make sure there's no difference.

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Calcium will never rise on its own in a reef tank without some sort of dosing or additive like PurpleUp, et cetera... 

I'd guess either fluctuations in salinity or time to order a new Salifert. FWIW Salifert is my favorite calcium test but there have been many times where I've had to discard half-used reagent bottles from strange anomalies. It does happen.

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