re: flourite

["Chrys" <chrys at addr_com>]

You can use up to a 50/50 mix of flourite/plain gravel  according to the instructions from Seachem.  I did this in my 48 gallon.  I used two bags of flourite, mixed with some similarly colored gravel.  I didn't do layers, I mixed.  Works just fine.
    On a 20 gallon, I personally would get one bag of flourite, and mix with gravel.  You save money and some rinsing that way.
    Of course, this is if you're on a budget. YMMv, IMHO, etc.
-Chrys