Randy Holmes-Farley
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My Tank Thread
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Okay, the quick google tells me STAX are mined limestone Oolite
Wikipedia tells me Oolite (for egg) is sedimentary rock formed from concentric spheric layers of (in no particular order) phosphate, clay, chert, DOLOMITE, or iron minerals.
Yes the same dolomite (Calcium Magnesium Carbonate) we often use in calcium reactors for Mg addition.
But at tank pH my guess would be that the Mg addition from quarried limestone is minimal?
Thoughts?
Dolomite can not explain the result because alk would be rising a huge amount. This is from one of my articles:
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+ + CO32-
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.