QUESTION:
Do fish droppings float to the top, float at the level in the tank when
made, or do they sink to the bottom?  

ANSWER from Michael Wiederhold on January 22, 1998:

Of course, fish DROPPINGS, by definition, DROP!  Seriously, generally fish
waste does drop, but quite slowly.  But a good group of snails should still
do a fine job of cleaning the tank.  The pond snails, Biomphalaria
glabrata, that we are working with can make themselve float or sink,
depending on how large a bubble of an air they keep inside of the shell.
When I was video-taping crawling patterns of snails on the rotating table,
if they wouldn't settle onto the table before we started it rotating, they
would float for several minutes and then pop out a small bubble every 20 to
30 seconds until they began to sink and settle to the bottom.  I'll bet
that if you put about six pond snails in the aquarium they will get to the
"food" eventually.  The snails will also do a good job of cleaning the
algae off of the walls of the aquarium and keep it clean looking.  Any two
snails (of the same species) will start to have babies after a week or so,
so you will want to keep the snail population down to a reasonable number.
If there are too many, they will stop breeding and deteriorate generally.
	Good luck.  Let me know how it all works out!
	I and my two technicians leave for the Kennedy Space Center next Tuesday
(Jan 27) to retrieve both snails and fish from the first flight of the
CEBAS system on STS-89, which is scheduled to launch tonight, if the
weather cooperates!