My Mg test must be wrong, right?

[don_chuwish]

Since rebuilding my 120G (see build thread linked in sig) and getting my BRS 2-part losers going and tuned to my mixed reef's consumption, I've noticed some confusing/troubling results with the Mg tests.
I'm dosing 120ml per night of both Ca and Alk (BRS 2-part). Keeping levels at around Ca 425, Alk 8.0.
Aside from a water change 5 weeks ago, I haven't added any Mg. But my Red Sea Mg tests keep returning a consistent 1400-1440 (trending UP slightly). This makes no sense to me. I don't see an expiry on the bottles, just a lot number, but I have had this kit quite a while.
Should I be suspicious of the test kit or is there another explanation?

 

[TUSI]

I would start with making sure the test kit is correct.

 

[HolisticBear]

But my Red Sea Mg tests keep returning a consistent 1400-1440 (trending UP slightly)

Some salts run high in Mg and unfortunately the Red Sea Mg also has a bad reputation for testing high. You'll find various threads here on that topic. A salifert Mg kit would only set you back $15 and you could compare the two results.

 

[Randy Holmes-Farley Verified Community Expert]

Agree with above. Don't worry much about it. The magnesium reflects what was in the salt mix, and even if 1400 ppm is accurate, it is fine.

 

[don_chuwish]

Thanks all, I just find it odd that it's not dropping at all, considering the consumption rates of Ca and Alk. But I guess I'll get a different test kit to compare against.

 

[Damien Buckley]

I found the RS Mg kit entirely worthless. I only ever got one test that wasn't off the scale (1600+). I sent off for an ICP. It came back with the Mg at 1317. I bought the NYOS Mg kit & it was almost smack-on what the ICP said so I tossed the Red Sea kit in the bin.

I use Coral Pro salt & the Mg now sits at 1450ish without any other dosing.

 

[AdamNC]

One thing I've noticed when my Mg levels don't seem right. Clean your vials, and not with just a rinse in water. Soak the vials in vinegar for a few mins and then use a q-tip to wipe out the residue. Rinse with RO/DI a few times, air dry upside down and your good. I've taken a test from over 1400ppm to its true reading of 1280p-1300ppm just by cleaning.

See my sig below.

 

[Havoks]

I use Red Sea test kits and by keeping your vials clean before and after test I haven't got any bad results. Any residue left in them will throw off your results

 

[Randy Holmes-Farley Verified Community Expert]

Thanks all, I just find it odd that it's not dropping at all, considering the consumption rates of Ca and Alk. But I guess I'll get a different test kit to compare against.

Actual consumption of magnesium is usually about 10% of the calcium depletion rate or less, depending on the organisms consuming calcium.

 

[don_chuwish]

One thing I've noticed when my Mg levels don't seem right. Clean your vials, and not with just a rinse in water. Soak the vials in vinegar for a few mins and then use a q-tip to wipe out the residue. Rinse with RO/DI a few times, air dry upside down and your good. I've taken a test from over 1400ppm to its true reading of 1280p-1300ppm just by cleaning.

See my sig below.

Thanks, yep, did that. It was perfectly clean. :-(

 

[don_chuwish]

Actual consumption of magnesium is usually about 10% of the calcium depletion rate or less, depending on the organisms consuming calcium.

Thanks! I didn't know that 10% figure. Handy fact!

 

[DarkSky]

I'm dosing 120ml per night of both Ca and Alk

I just wanted to comment and ask - are you dosing all 120ml in one shot? If you are, you might want to consider spreading the dose out over the course of the day to lower Ca/Alk swings. If you're dosing 120ml in a 120g volume, your Alk swings will be over 1.0 dKh.

 

[don_chuwish]

I just wanted to comment and ask - are you dosing all 120ml in one shot? If you are, you might want to consider spreading the dose out over the course of the day to lower Ca/Alk swings. If you're dosing 120ml in a 120g volume, your Alk swings will be over 1.0 dKh.

Thanks, yes I spread it out. BRS dosing pumps at 1.1ml/minute. I used reeftronics fantastic code generator to have the Apex do it between 8:00PM and 10:00AM, separating the two by 30 minutes:

Alk:
Fallback OFF
OSC 000:00/007:47/052:13 Then ON
If Time 10:00 to 19:59 Then OFF
If pH > 8.35 Then OFF
If FeedB 030 Then OFF
If Power Apex Off 000 Then OFF

Ca:
Fallback OFF
OSC 030:00/007:47/022:13 Then ON
If Time 10:00 to 19:59 Then OFF
If FeedB 030 Then OFF
If Power Apex Off 000 Then OFF

 

[don_chuwish]

Just a quick update - Salifert agrees with Red Sea. 1395.
But much easier test to do for sure.