[Dave P]

Not to be disputatious, but I have been using Equilibrium in "el Natural" tanks with some success, for me, anyway.

Indeed, the use of Equilibrium in 'El Natural' aquariums may not be problematic if the soil underlayer is mostly aerobic. What promotes an anaerobic microbial environment in submerged soils? I would have to think that the following would play a role:

1) Soil depth -- the deeper the soil layer, the greater the propensity for an anaerobic microbial environment.

2) Soil type -- denser soils, I would have to think, would limit the circulation of water throughout the soil layer, promoting an anaerobic environment.

3) Plant root density -- the roots of aquatic plants deliver oxygen to the surrounding rhizosphere. This favors an aerobic microbial environment. Fewer roots would mean smaller and more isolated rhizospheres which would in turn favor the anaerobic environment.

4) Water circulation -- if water circulation is poor in the water column, oxygenated water will have a harder time reaching the soil layer. This would promote an anaerobic environment.

If your aquarium has abundant plant growth with robust root penetration throughout the soil, sufficient water circulation, and a soil layer that is not too deep or too dense, then the use of Equilibrium may pose no problem at all.

However, if your aquarium differs in one or more of these conditions, then there is a greater chance that some of the sulfates contained within Equilibrium will be anaerobically reduced to H2S.

I think Diana was suggesting a solution to people "plagued" with soft water (I can't believe I just typed that... ), which would work regardless of the soil depth, soil type, root density and water circulation.

Is the amount of sulfate contained in Equilibrium considered "high"?

It's my understanding that *all* of the cationic species (Ca, Mg, Fe, Mn, K) contained in Equilibrium are bound to sulfate. It's nothing but sulfate salts.

Calcium chloride eliminates "potential" downsides, but it doesn't help to maintain the magnesium level, which is typically done, if needed, with epsom salts, a sulfate.

Since the desirable concentration of magnesium is considerably less than that of calcium, the amount of Epsom's salts needed to achieve this is likewise less. I guess if one was really concerned about limiting the concentration of sulfate, he/she could try to special order MgCl2, but this would be considerably more expensive than picking up a box of Epsom's salts from the drugstore. Alternatively, you could also use a product such as Seachem's Reef Advantage Magnesium, which is a combination of both MgCl2 and MgSO4.

Dave