Quote:
Originally posted by Billpers:
Q #1: One question that I have is, what happens to the SO4 when it splits from the CA?
***Plants will take up some sulfate for their sulfur needs (they need almost as much sulfur as magnesium). See "Critical Concentrations" on page 105 in my book.
The remaining sulfate diffuses throughout the water. I don't know of any sulfate salt that is insoluble. That's why Equilibrium probably dissolves very quickly. Dissolved salts (including sulfates) will diffuse into the substrate so that the concentration in substrate water will probably approximate what's in the water.
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While walking through swamps I've often encountered large amounts of H2S. (It can be easily identified without expensive lab equipment.  I wonder if high sulphates in the water by themselves are responsible for this or if there is some other process involved that grabs whatever sulphur is available to combine with the hydrogen. I don't know that, either.
***Bacteria use sulfates as their electron acceptor and convert the sulfates to sulfides (reaction on p. 67 my book). The sulfides readily combine with metals in soil like iron, zinc, manganese, etc to form precipitates. If there's no metals to precipitate out the sulfide, then you have H2S. That's why I got major toxicity when I added sulfate-contaning fertilizers to potting soil (made up mostly of organic matter and with very little metals), but got absolutely no toxicity when I added same fertilizer to my garden soil.
Brackish water swamps along the coast will have more H2S than freshwater swamps that are further inland. That's because ocean water contains lots of sulfates.
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It would be interesting to conduct an experiment with two natural tanks with anaerobic substrates and water with low sulfates. CaSO4 would be added to one and the amount of H2S measured. The point at which H2S becomes a threat would also have to be predetermined.
Bill
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Experiments are always fun. I would compare CaSO4 with CaCl2 (OR MgSO4 with MgCl2). The only variable then is the sulfate.
I was pleased with Seachem's response to your query. Thank you for posting it.