[Wet Thumb Forum]-BIG plant die off

[~SP~]

Taking into account short time of this dying off and vast diversity of affected plants (slow- and fastgrowers) I'd rather propose as a reason some fast drammatic change in water conditions, most probably pH, which is highly corresponds with very low carbonate hardness.
Although, I totally agreed with Diana about the necessity of supplying the plants with nutrients which are absent or scare in this regionaly specific kind of water.