Magnesium, Chloride vs Sulphate?

[OllieNZ]

Hi All,

I'm about to start dosing using Randy's 2 part recipes and was wondering why it includes Magnesium Sulphate vs just going with straight up Magnesium Chloride?

Regards

Ollie

 

[Randy Holmes-Farley]

Because if you dose only the chloride form, it has a tendency to boost chloride relative to sulfate, and over time the chloride rises and the sulfate falls (at fixed salinity). That is especially pronounced if you are also using calcium chloride.

 

[OllieNZ]

Because if you dose only the chloride form, it has a tendency to boost chloride relative to sulfate, and over time the chloride rises and the sulfate falls (at fixed salinity). That is especially pronounced if you are also using calcium chloride.

Thanks for taking the time to reply yourself Randy!

That leads me on to the following then..... What impact does high chloride vs low sulphate have on the aquarium?

I have both forms and will be making the mix per your instructions, I'm just trying to understand the why especially when most off the shelf mixes seem to be Magnesium Chloride only.

 

[Randy Holmes-Farley]

Thanks for taking the time to reply yourself Randy!

That leads me on to the following then..... What impact does high chloride vs low sulphate have on the aquarium?

I have both forms and will be making the mix per your instructions, I'm just trying to understand the why especially when most off the shelf mixes seem to be Magnesium Chloride only.

Chloride (Cl-) and sulfate (SO4--) are far and away the two highest concentration negatively charged ions in seawater. The ocean is quite well fixed in the ratio, but artificial seawater mixes vary a bit.

Scientists rarely study the effect of an off ratio as it doesn't happen in the ocean (it may in an estuary with low salinity from a river input), and so there is not much info on what an off ratio does. I do not think it is critical, but taking normal seawater as a guide, it is prudent to stay somewhat close to the NSW ratio.

http://reefkeeping.com/issues/2005-11/rhf/index.php

Figure 3. Relative concentration of ions in seawater by weight.