Mg Always High

[BigMax]

My tank has been up for 7 years and I 've never needed to dose Mg. My question is why? Some specifics:

1) 70 Gallon mixed reef tank (total system has 70 gallons of water, when including sump).
2) Dosing BRS 2 part 55ml soda ash and 55ml calcium chloride each day.
3) 12 gallon water change every other week (I/O Reef Crystals)
4) Alk 8.3
5) Cal 455
6) Substrate Carib Sea live sand.
7) Mg 1750 ppm (Tested via Hanna and Salifert). And always that high.
8) 120 lbs of live rock.

Is the salt mix providing to much Mg? Seems odd if I still need to dose 55ml of 2 part daily?

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[Koty]

Maybe your salinity is off?

 

[Randy Holmes-Farley]

I'm skeptical that the result is accurate. Have you tried those kits on your new salt water?

What do you think the salinity is?

 

[BigMax]

I'm skeptical that the result is accurate. Have you tried those kits on your new salt water?

What do you think the salinity is?

I'll check that next time I brew, this week. Tank salinity is 1.026.

It does seem odd that I got 1750 from the Hanna yesterday and the Salifert did not change color, added the entire syringe, so therefore above 1500.

 

[BigMax]

You gave me something else to thing about. I'm in MN and the tank s in the basement the room is 64 degrees. The tank is 76.5. I use a refractometer with ATC but the instrument is at room temp and the tank is 76.5. maybe I need to warm the refractometer, bringing it up to the main level of the house and get it up to 70 degrees before testing?

Also, all the reagents would be 64 as well....likely a problem, but I would have thought it would be insignificant? as the reagent added at 64 degrees. is a very small portion of the test vial when adding the 76.5 degrees tank water?

 

[Randy Holmes-Farley]

You gave me something else to thing about. I'm in MN and the tank s in the basement the room is 62-64 degrees. The tank is 76.5. I use a refractometer with ATC but the instrument is at room temp and the tank is 76.5. maybe I needed to warm the refractometer up to the main level of the house and get it up to 70 degrees before testing?

If it has ATC, the temp should not matter within the ATC range, but letting it warm a bit before use is not a bad thing to try.

 

[BigMax]

If it has ATC, the temp should not matter within the ATC range, but letting it warm a bit before use is not a bad thing to try.

Thanks Randy!

I edited my last question and added this:

Also, all the reagents would be 64 as well....likely a problem, but I would have thought it would be insignificant? as the reagent added at 64 degrees. is a very small portion of the test vial when adding the 76.5 degrees tank water?

 

[Randy Holmes-Farley]

Thanks Randy!

I edited my last question and added this:

Also, all the reagents would be 64 as well....likely a problem, but I would have thought it would be insignificant? as the reagent added at 64 degrees. is a very small portion of the test vial when adding the 76.5 degrees tank water?

For a titration test like magnesium, temp should not be a big issue.

 

[homer1475]

I hardly have to add mag either. Similar tanks sizes, and I use IO for a weekly 20G change.

80G display with 30G sump = 85 total water
dose 128ml a day of randys DIY 2 part
I'm usually in the 1500 to 1600 range.

For salifert kit, just suck up another 1ml of reagent, and add the results.

I just got the hanna for mag last week, and am finding it very comparable in results to salifert.

Any issues with inverts? 1700 is pretty high and usually starts to slow down inverts at that level.

 

[BigMax]

I hardly have to add mag either. Similar tanks sizes, and I use IO for a weekly 20G change.

80G display with 30G sump = 85 total water
dose 128ml a day of randys DIY 2 part
I'm usually in the 1500 to 1600 range.

For salifert kit, just suck up another 1ml of reagent, and add the results.

I just got the hanna for mag last week, and am finding it very comparable in results to salifert.

Any issues with inverts? 1700 is pretty high and usually starts to slow down inverts at that level?

Thanks for the reply.

The only inverts I have are Mexican turbo snails, and they don't seem to last long, but I assumed it's just their nature? Lot's of bristle worms that came in with the live rock and they're very happy, unfortunately.

This is a shot of the tank from 2 years ago. The only thing that has changed is that the hammer has tripled in size, and now occupies several locations within the tank. It started out as a tank to cure live rock for my FOWLR tank, and I thought lets just try a coral for fun .... then stuff just happens. Not particularly proud of the tank , but it's still fun.

 

[BigMax]

Based on questions (thanks) I received here are several additional pieces of information:

- Salinity of tank is 1.026 (35ppt) calibrated refractometer prior to testing.
- Brewed water (I/O Reef Crystals) Mg measured 1700 ppm. (water change - yesterday)

Again, tank Mg measures 1700- 1750 ppm (both Salifert and Hanna)

So, I will assume the bi-weekly water changes are the primary contributor to high Mg as there may be batch to batch variation. 55 ml, of each, 2 part is added daily. So, unless other water changes were pushing 2000 ppm of Mg there is no explanation for how I got there.

I have 4 buckets of Reef Crystal to use up. I will likely switch to std IO when it's gone, or may alternate between the two mixes until the Reef Crystals are gone.

One additional question. It was noted that inverts may not like the high Mg. Any other concerns?

 

[Randy Holmes-Farley]

Based on questions (thanks) I received here are several additional pieces of information:

- Salinity of tank is 1.026 (35ppt) calibrated refractometer prior to testing.
- Brewed water (I/O Reef Crystals) Mg measured 1700 ppm. (water change - yesterday)

Again, tank Mg measures 1700- 1750 ppm (both Salifert and Hanna)

So, I will assume the bi-weekly water changes are the primary contributor to high Mg as there may be batch to batch variation. 55 ml, of each, 2 part is added daily. So, unless other water changes were pushing 2000 ppm of Mg there is no explanation for how I got there.

I have 4 buckets of Reef Crystal to use up. I will likely switch to std IO when it's gone, or may alternate between the two mixes until the Reef Crystals are gone.

One additional question. It was noted that inverts may not like the high Mg. Any other concerns?

IMO, these are thoughts on why the mag seems high in order of decreasing likelihood. I'm trying out a new way to give my thoughts with percentages associated with my opinion of likelihood. lol

1. The test kits are off and magnesium is lower than you think. Mag kits are frequently inaccurate. I'd rate this as >50% chance of being the explanation despite using 2 methods.

2. The salintiy is higher than you think in both cases. It would need to be pretty high though. This is worth pursuing more due to salinity than the magnesium. I'd rate this explanation as 15% chance.

3. Salt mix has settled and is inhomogeneous. Explains the new salt water but not the tank. 5% chance.

4. Bad batch of salt mix with too much magnesium. Would need to have happened over multiple buckets to get the tank that high. 5% chance.

5. Something else unknown 2% chance.

As a general rule, IMO, people overestimate the chance of bad batches of salt and underestimate the chances the testing is inaccurate for some reason when trying to explain large deviations from expected norms.

 

[BigMax]

IMO, these are thoughts on why the mag seems high in order of decreasing likelihood. I'm trying out a new way to give my thoughts with percentages associated with my opinion of likelihood. lol

1. The test kits are off and magnesium is lower than you think. Mag kits are frequently inaccurate. I'd rate this as >50% chance of being the explanation despite using 2 methods.

2. The salintiy is higher than you think in both cases. It would need to be pretty high though. This is worth pursuing more due to salinity than the magnesium. I'd rate this explanation as 15% chance.

3. Salt mix has settled and is inhomogeneous. Explains the new salt water but not the tank. 5% chance.

4. Bad batch of salt mix with too much magnesium. Would need to have happened over multiple buckets to get the tank that high. 5% chance.

5. Something else unknown 2% chance.

As a general rule, IMO, people overestimate the chance of bad batches of salt and underestimate the chances the testing is inaccurate for some reason when trying to explain large deviations from expected norms.

Thanks Randy, much appreciated! Very good way to approach it.

I see Hanna makes standards for their Mg tester. May be worth a try to to test for accuracy and repeatability, at least against a std.

 

[Randy Holmes-Farley]

Thanks Randy, much appreciated! Very good way to approach it.

I see Hanna makes standards for their Mg tester. May be worth a try to to test for accuracy and repeatability, at least against a std.

Sort of. Their "standards" are not really standards for testing the reagents and procedures as would be a true standard. They are just colored water to test the electronics.

 

[BigMax]

Sort of. Their "standards" are not really standards for testing the reagents and procedures as would be a true standard. They are just colored water to test the electronics.

Is there anyway to validate reagents by creating a quasi standard in distilled water with a known amount of magnesium chloride at x purity and some sodium chloride to create a 'seawater' mix?

The only thing I can come up with is to have 2 sets of reagent, test them against each other for relative accuracy and repeatability. Then send in a aquarium sample to ATI, or such, and make corrections based on their testing? Always having 2 sets on hand to continually have a pass down reference, as long as it's well within the expiration window. Then repeat the lab testing process again at some point to avoid compounding of marginal error.

Honestly, considering aging of reagents and hobbyist kit quality as the described in above, doing anything unique is probably wishful thinking. But, I'm curious whether someone has a solution? My guess is overall it's not that important, and being in the ballpark is acceptable for the hobby, but it still bugs me

 

[Koty]

I would put 4 before 3. Went through this ordeal and found out that my Aquaforest bucket was badly mixed. I also found that their claim that they do ICP is questionable IMO.
I moved to Fauna Marine ...the less costly german co.

 

[Randy Holmes-Farley]

I would put 4 before 3. Went through this ordeal and found out that my Aquaforest bucket was badly mixed. I also found that their claim that they do ICP is questionable IMO.
I moved to Fauna Marine ...the less costly german co.

That could be. I just am not seeing how inhomogeneous buckets can get a tank larger than a bucket to have very high mag.

 

[Randy Holmes-Farley]

Is there anyway to validate reagents by creating a quasi standard in distilled water with a known amount of magnesium chloride at x purity and some sodium chloride to create a 'seawater' mix?

The only thing I can come up with is to have 2 sets of reagent, test them against each other for relative accuracy and repeatability. Then send in a aquarium sample to ATI, or such, and make corrections based on their testing? Always having 2 sets on hand to continually have a pass down reference, as long as it's well within the expiration window. Then repeat the lab testing process again at some point to avoid compounding of marginal error.

Honestly, considering aging of reagents and hobbyist kit quality as the described in above, doing anything unique is probably wishful thinking. But, I'm curious whether someone has a solution? My guess is overall it's not that important, and being in the ballpark is acceptable for the hobby, but it still bugs me

Fauna Marin makes a reference standard, though I do not know anything about its reliability.

Fauna Marin Multi Reference is a Standard for Much More Than Salinity | Reef Builders | The Reef and Saltwater Aquarium Blog

Multi Reference by Fauna Marin is the first product of its kind that helps reefers really dial in their chemistry, by testing the tests. WhereTwo Little Fishies’ AccuraSea and Brightwell Aquatics’…

reefbuilders.com

 

[BigMax]

Fauna Marin makes a reference standard, though I do not know anything about its reliability.

Fauna Marin Multi Reference is a Standard for Much More Than Salinity | Reef Builders | The Reef and Saltwater Aquarium Blog

Multi Reference by Fauna Marin is the first product of its kind that helps reefers really dial in their chemistry, by testing the tests. WhereTwo Little Fishies’ AccuraSea and Brightwell Aquatics’…

reefbuilders.com

That's very interesting. I'll definitely check it out.