I don't run around advocating for this system much, in fact have only mentioned it one time in another thread when I thought it might help someone with a problem in there tank.  

Its easy, cheap, and works.

As for Vodka vs vinegar and growth of unwanteds, the two compounds enter metabolism in quite different points with the most likely outcome in the catabolic use of ethanol being conversion in the cell to.... acetic acid... or vinegar in two steps!  Ethanol actually has a bit more "energy" (because the two steps to get to acetic acid release energy the cell uses) in it so depending upon the organism in question, the prevalence of the required metabolic enzymes its propensity to bloom under supplementation of one or the other may change markedly with ethanol providing more "bang" for the buck.  Asside from the fact that the vinegar most people use is much less concentrated than the vodka most people use (from a # of molecules in a given volume standpoint) the vodka is also higher "octane" with respect to revving up metabolism with energy.  

So... a given dose of vodka is both more concentrated and more powerful metabolically.  Thus things tend to or would be expected to (is probably the more appropriate phrasing) bloom a bit more robustly under vodka supplementation.

You need to replace snails about every 6 months. For me, about half of mine die every 3 months and I replace those.

This is part of the problem. You have NOTHING to eat your algae.