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Unread 07/07/2012, 10:23 AM   #1
Spar
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Different Mg readings - Salifert vs Red Sea Pro

Not that this is a huge difference, just wondering which is best to go with.

I get about a 80-100ppm difference between my Salifert and Red Sea Pro Mg testkits.

This morning reading for example:
Salifert = 1280
RSP = 1380

Should I take 1/2 the difference? Or is one more reliable than the other normally?


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Unread 07/07/2012, 10:29 AM   #2
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It could also be operator error, a known variable in any test. Not a negative thing, it's just something to expect and acknowlege.

If I am truly curious, and I most often am , I would do 3 separate tests each for Salifert and Red Sea Pro, all in one sitting, and then compare.


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Current Tank Info: Incept 3/2010, 150 RR, 50g sump, 20g fuge, 150w 15K MH x3, T5 actinics x8, moonlight LED x6, 1400gph return, Koralia 1400 x4, 300 g skimmer, 4 tangs, 2 mandarins, 2 perc, 6 line, 3 cardinals, 2 firefish, SPS, LPS, zoas, palys, shrooms, clam
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Unread 07/07/2012, 10:38 AM   #3
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Possibly, but it has been doing this for some time now, consistently different in reading. Even consistent when the reading was much higher. Used to get 1580 vs 1500.

But will test again to make sure. I have always hated the droppers with the Salifert testkits as always question the consistency of each drop and sometimes I suspect that 2 drops came through at the same time. Wish they would get higher quality ones.

If I dose to bring Mg back to 1450 using the average of the two, then it is possible Mg is actually either 1500 or 1400. Either way should be fine right?


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Unread 07/07/2012, 10:40 AM   #4
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Get a solution with a known magnesium level and check with both kits to see which one is right.


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Unread 07/07/2012, 10:47 AM   #5
Spar
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Quote:
Originally Posted by disc1 View Post
Get a solution with a known magnesium level and check with both kits to see which one is right.
smart idea. i can just mix my own solution using RO/DI. will post back my results.


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Unread 07/07/2012, 11:39 AM   #6
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Well tried with 1/2 gallon + 1 TBSP epsom salt but neither result looked right... probably need to try with a larger measurement. Will do another time.


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Unread 07/07/2012, 12:32 PM   #7
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I just ran the tests on my tank 3 times each. Each test was within 20ppm of the last test.

Salifert - Averaged 1220 (noting 60 less than the test I did originally)
RSP - Averaged 1340 (40 less than the original test)

So with that there is a 120ppm difference. Both are fairly new. <1 Year on the Salifert (exp listed of 6/2013), and <3 months on the RSP.


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Unread 07/07/2012, 12:59 PM   #8
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Quote:
Originally Posted by Spar View Post
smart idea. i can just mix my own solution using RO/DI. will post back my results.
LOL!! You gotta be a chemist to come up with that one!

Quote:
Originally Posted by Spar View Post
I just ran the tests on my tank 3 times each. Each test was within 20ppm of the last test.

Salifert - Averaged 1220 (noting 60 less than the test I did originally)
RSP - Averaged 1340 (40 less than the original test)

So with that there is a 120ppm difference. Both are fairly new. <1 Year on the Salifert (exp listed of 6/2013), and <3 months on the RSP.
From a practical standpoint, I wouldn't sweat it. Between the two tests, you've pretty much bracketed the acceptable levels for mag (1250-1350). What's the chances of that? LOL! You may want to raise it a bit, but so long as you are not having trouble with your alk and calcium levels, your current mag should be fine. I've gone as high as 1550 by dosing and too lazy to check, and had no issues.

From a chemist or perfectionist standpoint, it kinda sucks to have such a widely disparate result between two "precision" tests. Guess anything more precise may be too expensive for a hobbyst, though.


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Anything I post is just an opinion. One of many in this hobby. Believe and follow at your own risk of rapid and complete annihilation of all life in your tank :)

Current Tank Info: Incept 3/2010, 150 RR, 50g sump, 20g fuge, 150w 15K MH x3, T5 actinics x8, moonlight LED x6, 1400gph return, Koralia 1400 x4, 300 g skimmer, 4 tangs, 2 mandarins, 2 perc, 6 line, 3 cardinals, 2 firefish, SPS, LPS, zoas, palys, shrooms, clam
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Unread 07/08/2012, 07:14 AM   #9
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Quote:
Originally Posted by Spar View Post
Well tried with 1/2 gallon + 1 TBSP epsom salt but neither result looked right... probably need to try with a larger measurement. Will do another time.
This would only work if you are sure that the epsom salt is a truly homogeneous mixture. I would think you would need lab grade salt for a test like this.


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