Help with dosing (especially Mg depletion rate)

[potatocouch]

I have a quick question for @Randy Holmes-Farley and co

I feel that my Mg depletion rate is high.
Alk depletion rate is probably at normal size.
And as you know, my Ca depletion rate is fairly low.

My previous question was about Ca depletion and @Randy Holmes-Farley , you have explained that with my live stock, it is normal to replenish just via weekly WC.

But what I'm confused about is my Mg depletion ....

Please refer to the following stats for reference:

I have 55 gallons tank and dose using Red Sea foundation A, B and C.

I've calculated the dosing and its impact to my tank:

• 20 ml of C will raise 11 Mg.
• 5 ml of B will raise 0.3 kH.
• 20 ml of A will raise 22 Ca.

If you look at the Mg columns above:

• Weekly WC was done on 26/02/2016, which brings Mg level to 1300.
• Then test was done on 28/02/2016, reading on Mg was 1260.
• 20 ml dose was then done on 28/02/2016.
• 40 ml dose was then done on 29/02/2016.
• 20 ml dose was then done on 1/03/2016 morning.
• Test was done on 1/03/2016 evening, reading on Mg was 1320.
• Test was done the next day (2/03/2016) afternoon, reading on Mg was 1270.
• That is a drop of 50 ppm of Mg in just 1 day.

It doesn't sound right, does it? especially when the tank doesn't have clam and only has 1x torch, 1x goniopora, 2x hammers, colony of zoanthids (I just added few more frags), colony of turbo snails, 1x anemone and 4 fishes.

Any input/s are much appreciated.

I'm a tad confuse about what is my Mg depletion rate and how much exactly should I dose for Mg.

For Alk, I think 5 ml per day is the right amount to keep kH at 8.3 ~ 8.5.
For Ca, weekly WC should replenish it to the right amount at 420.

Charting provided as reference:

 

[Randy Holmes-Farley Verified Community Expert]

Magnesium consumption is usually about 1/10th or less of the calcium consumption rate, depending on what organisms are using magnesium and calcium. If it is much higher, there is an issue of some sort (usually testing) that is not actual consumption.

If water changes maintain calcium, then it will also maintain magnesium. There's not much that can cause deviations from that.

Magnesium never, ever drops 50 ppm in one day. It might drop that much in a few months. That drop is definitely testing error, unless you did a big water change with a low magnesium salt mix.

FWIW, many people have problems with magnesium testing, and my expectation is that the variations in your values reflect testing error, not real changes.

What kit are you using?

FWIW, the Red Sea magnesium kit seems especially prone to problems for reasons I do not know.

 

[Randy Holmes-Farley Verified Community Expert]

What salt mix are you using?

 

[potatocouch]

What salt mix are you using?

Red Sea Salt

My aim is the red above (35 ppt ~ 1.026 SG).

 

[potatocouch]

What kit are you using?

Salifert with expiry date of 2020.

FWIW, the Red Sea magnesium kit seems especially prone to problems for reasons I do not know.

I prefer off-the-shelf product (no mixing), what brand of Mg supplement would you recommend other than Red Sea C?

 

[httorihanzo]

Side track, I just stole your excel format for tracking. Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

Salifert with expiry date of 2020.



I prefer off-the-shelf product (no mixing), what brand of Mg supplement would you recommend other than Red Sea C?

Meaning it must be a liquid?

Lots of them are suitable. I'm not aware of any that are not, although some may have inaccurate claims.

I would not overthink what is most likely just testing problems. Boosting the Red Sea salt by 50-100 ppm magnesium before you use it should allow you to not have to measure or dose it in the tank.

 

[potatocouch]

I would not overthink what is most likely just testing problems. Boosting the Red Sea salt by 50-100 ppm magnesium before you use it should allow you to not have to measure or dose it in the tank.

I think you're right .... I shouldn't be overthinking this .. most likely I got a feeling it's testing error too ... I shall test again few times. Thanks @Randy Holmes-Farley !

Side track, I just stole your excel format for tracking. Thanks!

Hey! you gotta pay for that ... it's trademarked.... LOL ... joking ... go for it, man. I think it can be expanded in such way ...sometimes testing date and dosing date a tad confusing.