I recently set up a new tank, a 60 gallon high.  For the substrate this time around I used laterite and flourite in the bottom 1/3 and a mix of a small and medium sized gravel.  So far my plants are growing well in it.  The only downfall I see with this mix is that the smaller and larger gravel might mix together and compact, so far this hasn't really happened.  Hopefully the plant rootes will keep it from compacting  The larger gravel I used also makes it a bit hard to plant stem plants individually into the substrate.  This might prove easier as it mixes with the smaller gravel.  The total thickness of the substrate is about 5 inches.

In my old 29 gallon tank (that the 60 replaced) I used only flourite on the bottom.  My plants grew well with it, but it was very dusty and I often had a cloudy tank after I did maintenance.  It also chewed up the barbels and whiskers on any catfish or botias I got.  The roughness of it is why I chose not use it as my main substrate in my 60 gallon tank.   

In a 29 gallon display tank I set up I used straight black sand, about 1 1/2 inches deep.  There is mostly just stem plants in this tank.  The sand works well to hold them down, but it is to fine of a sand and compacts.  I try to periodically stir portions of it to prevent anaerobic bacteria pockets.  Debri also sits on top and it really only looks clean right after I have syphoned stuff off of the top.  If it was a sand with bigger particles I think it would work better.  The black color does make the plants and fish look really nice.  I chose not to put laterite or anything under the sand as stem plants get a lot of their nutrients through absorption through their leaves.  I would like to set up a tank in the future with a slightly large grained black sand.

In yet another display tank I did, I have it set up with laterite underneath medium sized gravel.  There are only crypts and anubias growing in this tank.  They seem to do well with this substrate.  The substrate is about 4 inches deep.

In a 75 gallon display tank there is only about 5 inches of medium sized gravel.  The plants that do grow in this tank do very well, but there is not much diversity in plant life. 

In his blog, Don, talks about helping Paul set up his new tank with a mix of builders sand and aquatic plant soil.  I am interested to see how it does.  You can read his blog post here: http://www.aquariphiles.com/dalbrecht/weblog/6.html

I am eager to try a tank with top soil in it.  I have read many good things about having a layer of soil underneath the gravel.  This and other substrate experiments will have to wait until I have room for more tanks though!

What substrates have you used and what are your experiences with them?