I have used fine sand (as opposed to gravel) as a substrate for years.
Here's a summary of advantages:
1. Inert. Does not affect pH or (apparently) leach anything into the
2. Cheap. Less than $5 for a hundred pounds at the hardware store.
3. Attractive. Light brown flecked with dark bits and not blinding
4. Accomodating. All plants I've grown have developed ENORMOUS root
systems very quickly. Corydoras love to root around in it.
5. Convenient. Crud (uneaten food, fish poop, etc.) sits on top and
is easily vacuumed off.
1. Because of compromised water movement, may become anaerobic. One
time I set up a tank with a bit of a nitrogen source (sterilized
composted cow manure) in the substrate. Despite lots of plants, H2S
was produced, which fed a never-ending bloom of sulfur-metabolizing
bacteria and caused permanently cloudy water. After many gyrations I
finally gave up and tore down this tank and started over.
2. Right now the substrate in my tank is almost a solid mass of
roots. Impossible to pull anything out without disrupting the entire
tank. Large Echinodorus have roots from one end of the tank to the
other. Growth slows down after a while except in the very well rooted
plants, which continue to flourish. I have a some gorgeous sword
plants (E. osiris. E. bleheri, E. martii, E. uruguayensis) which
still produce new leaves every few days. It seems that new plants
don't adapt well. Inflexibility
3. Possible long term instability.
Like many others, I'd like to address this last point. and try heating
coils at some point. It would seem that the small grain size of sand
would inhibit water movement, and simply produce a conductive rather
than a convective situation. Would it be possible to induce slow
flow through fine sand? Would a switch to larger grain size gravel be
necessary for heating coils to work properly?
What do y'all think?
National Fish & Wildlife Forensics Laboratory
Bob_Hoesch at fws_gov