Magnesium consumption

[Funston07]

Okay so I got a fairly new tank, roughly 2 months old. Started it with dry rock, live sand, and a bottle of Bio-Spira. Currently have 1 diamond goby, 2 clowns, cleaner shrimp and some snails. Also have about 20 frags and a BTA. Usually dont test mag as frequently as alk or cal but lately my mag is being consumed faster than even my alk. Im not having trouble keeping parameters stable but Im definitely having to dose mag more than anything else. I've been testing it weekly as of right now to make sure everything stays consistent. Just curious of what could be causing this, usually mag is consumed the least of the major 3.

 

[Randy Holmes-Farley Verified Community Expert]

How much did you need to dose in ppm?

A tiny amount will bind to bare calcium carbonate. Likely not enough for you to detect.

Test error is very common.

there is no other way to deplete magnesium without depleting ten times as much calcium and a ton of alkalinity.

 

[Funston07]

How much did you need to dose in ppm?

A tiny amount will bind to bare calcium carbonate. Likely not enough for you to detect.

Test error is very common.

there is no other way to deplete magnesium without depleting ten times as much calcium and a ton of alkalinity.

See thats what had me scratching my head cause my alk and cal have stayed the same with almost no dosing in between WC. I would say in the past week had to compensate for roughly 80-120ppm. During this time I havent had to dose anything for alk or cal though. I know its not a significant amount but considering my alk and cal staying the same it had me confused. Like you said though, possible test error. Cant fully rule that out, I use salifert test for mag and .02ml is about 20ppm difference which isn't hard to miscalculate from one week of testing to the next.

 

[Randy Holmes-Farley Verified Community Expert]

See thats what had me scratching my head cause my alk and cal have stayed the same with almost no dosing in between WC. I would say in the past week had to compensate for roughly 80-120ppm. During this time I havent had to dose anything for alk or cal though. I know its not a significant amount but considering my alk and cal staying the same it had me confused. Like you said though, possible test error. Cant fully rule that out, I use salifert test for mag and .02ml is about 20ppm difference which isn't hard to miscalculate from one week of testing to the next.

I guarantee there is zero chance the tank consumed 80-120 ppm magnesium and no calcium or alkalinity in a week. There's just no possibility except test error, which is VERY common for magnesium testing.

Changes in salinity will make all of these move up and down together, but since magnesium has the highest concentration, it moves the most on a pure ppm basis. About 3x as much as calcium.

 

[Funston07]

I guarantee there is zero chance the tank consumed 80-120 ppm magnesium and no calcium or alkalinity in a week. There's just no possibility except test error, which is VERY common for magnesium testing.

Changes in salinity will make all of these move up and down together, but since magnesium has the highest concentration, it moves the most on a pure ppm basis. About 3x as much as calcium.

You know now that you mention the salinity having that type of effect it is possible that's what gave me the initial lower reading. I just topped off the tank shortly before I got that lower reading and my cal was also about 5-10ppm lower than what I normally run it at. Factor that in with the accuracy of testing with salifert and I can totally see testing being the issue. Thanks for the input and helping me see what was going on from a different perspective. Gotta do my WC tomorrow so I'll double test and make sure everything is where it should be.