Adding Mag Chips to the degas chamber

Alabamareef · Nov 19, 2014

My Mg seems to never want to get above 1320. I've been looking and someone suggest to use Mg chips. I have a Ca reactor and teh effluent goes into a degas chamber then into the aquarium. I was considering putting chips into the degas chamber. I'm not wanting to do this to raise pH. My pH is 8.3, just want my Mg around 1400. Just want to know if this is a good idea and what I need to get.

Randy Holmes-Farley · Nov 20, 2014

I'd mix 10% dolomite in with the regular media rather than relegating it to the second chamber where it may not dissolve enough.

That said, this method cannot be used to boost magnesium because alkalinity would get too high. Use a supplement to boost it to where you want it, and the dolomite to keep it there.

Randy Holmes-Farley · Nov 20, 2014

Here's more on why you cannot use dolomite to boost magnesium (only maintain it):

It has been suggested that adding dolomite to CaCO₃/CO₂ reactors can help with magnesium problems. Dolomite is a material that contains both magnesium and calcium carbonate. If dolomite is being added to the reactor to maintain existing appropriate magnesium levels against the continual depletion via calcification (for example, if the calcium carbonate being used is too low in magnesium to maintain adequate magnesium) then this is a fine approach.

However, this method is unsuitable if the goal is to raise magnesium levels. The problem is that for every magnesium ion released from the dolomite, 2 units of alkalinity are also released:

MgCO₃ → Mg²⁺ + CO₃^2-

Consequently, if one wants to raise magnesium by 100 ppm, the alkalinity will necessarily rise by 8.2 meq/L (23 dKH). The only way around this problem is to add a mineral acid (not vinegar) to the aquarium to reduce the alkalinity, and that may be more problematic than just adding magnesium in the first place.