Heating Coils/Substrates

> From: Bob_Hoesch at mail_fws.gov
> 3.  Possible long term instability.
> Would a switch to larger grain size gravel be 
> necessary for heating coils to work properly?

In "The Optimum Aquarium", Horst and Kipper suggest that their first
freshwater 10,000 liter "Perfect Aquarium" only lasted 11 years (!)
because the substrate became too dense (page 175).  They had started
with relatively coarse gravel (4 mm) and figured that detritus was
able to work its down into the spaces, was mineralized by bacteria and
essentially became "cement".  They went to 2-3 mm gravel in the
"Optimum Aquarium" (1.2 tons of it mixed with 25 liters of laterite
in a layer 10-23 cm thick).

A sand substrate would not allow detritus to sink and and decompose.
On the other hand, it may be too dense to start with.  Plants
obviously like it but the question of long term effects has not been

How long have your sand-substrate tanks been set up?  The Echinodorus
are obviously happy.