unusual for mts deaths. i couldnt kill mine if i tried. must be something in your bag of AS2. maybe it got fumigated or something in shipping. flowers will not notice the difference, i used old as for some and to be honest, plain ole dirt is better.
as for the original post, i actually went the other route with my daughters 20L and capped AS1 with eco. i dont like plant growth with eco, but i prefer its consistancy to AS, easier to keep plants down, especially with the may cories in her tank.