Snipe....I don't see why you could not use Sodium Carbonate or bicarbonate with alum....the only purpose of the buffering agent is that it makes the acidic alum, pH neutral. I do know from real world experience, the Alum amount required will be higher if broadcast spreading dry alum, regardless of what the pre-packaged products claims on application rates state. This fact is simply due to how Alum works when falling through the water column. FWIW, Alum with Hydrated Lime is a net +6 ionic charge. There are aluminum polymers in liquid form that do not effect water pH when applied, but the cost is as much as 4 times the dry Alum/H-Lime combo cost, yet the liquid polymers are applied faster, and have as high as a +14 ionic charge. In LARGE bodies of water, the labor cost savings on the application time required could make the liquid more cost effective.
As to why the pre-packaged flocculants use sodium carbonate or bicarbonate over H-Lime is probably due to it not forming a paste or because it is easier to produce the buffered pellets in a factory setting....I have no clue as to why either. What worries me with sodium carbonate or bicarbonate is, at a 20-40% rate by weight, it can not chemically offset the acidic value aluminum sulfate has...buffer %'s, as stated on MSDS labels, would not be a balanced chemical equation and would "theoretically", result in a pH drop. Real world application often defies the theory though, and the pre-packaged products are often used, though at much higher than claimed application rates they state for desired results. Calcium Hydroxide (Hydrated Lime) is FAR more caustic than either of the other buffers. And Hydrated Lime is required at a 42-50% by weight ration to become pH neutral....Chemically, carb and bicarb can not balance the Aluminum Sulfate's pH to neutral.
I guess now I am wondering why you want to apply Alum if you have no colloidal clay issues....are you wanting to bind available phosphorus in the pond?
