Magnesium dropping fast.

[$hing$hong]

Now my tank is currently 7 months old with only frags of zoanthid, ricordea and anacropora.
The problem is the magnesium was stable for the past 6 months at 1290ppm then this month it suddenly dropped to 1140ppm (Also with addition of GHA growth and dying chaetomorpha, not sure if its related to my Mg problem).
I only dose PartB (Baking Soda) to maintain the alkalinity and didnt dose any PartA(Calcium Chloride) due to no measurable Ca intake. I do not run any reactors (no activated carbon/GFO/zeolite). I only do 5% water change monthly due to limited space and location of the tank.

The question is how do I dose Mg back up? Is it better to raise Magnesium by Magnesium Chloride alone or Magnesium Chloride + Magnesium Sulfate mixture?

Parameters:
Salinity: 34ppt /1.025sg
pH:8.2
kh :7.3 dkh
Ca: 420ppm
Mg:1140ppm
NO3: 6.8ppm
PO4: 0.03ppm

Thankyou in advance for any inputs, this is my first time dosing 2-parts so any advice is welcome.

 

[Randy Holmes-Farley Verified Community Expert]

The observation is either test error or a salinity drop. Magnesium never drops faster than about 1/10th of the calcium consumption.

I suggest not even measuring it:

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

 

[$hing$hong]

The observation is either test error or a salinity drop. Magnesium never drops faster than about 1/10th of the calcium consumption.

I suggest not even measuring it:

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

Thankyou Randy, the thread you posted gave me a peace of mind by ignoring the test kit (for now).

Also nice to see you are still active in the hobby, I remember seeing you in Reefcentral 14-15 years ago when I was in the hobby.