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Allelopathy or Why it's important to have lotsa plants


             **  More plants == less algae! **

One of the most vexing problems facing aquarists attempting to setup
plant tanks for the first time is the plague of algae that inevitably
results when you increase the lighting level of a tank. We have been
advocating the use of LOTS of floating and fast growing plants at this
time ostensibly to compete with the algae for light and nutrients.

A recent article in TAG sheds new light on this old problem (sorry for
the pun; couldn't resist :-) Another reason or perhaps the real reason
why lots of plants in a new tank discourages algae growth is that many
plants release allelochemicals into the water which may suppress the
growth of many of the algaes. The article explains that the main purpose
of these chemicals (most of which stay in the plant) is to discourage
herbivores from eating the plant. When plant leaves die, these phenols
are liberated almost completely. Ever notice how snails prefer to feed
on older, dying leaves? Maybe they taste better because the allelo-
chemicals are gone! The author goes on to point out that there is
evidence that allelopathic compounds may accumulate in aquarium water
which explains why older aquariums with more plants have fewer algae
problems. I'm looking forward to Part 2 of the article in October!

Now I wonder what happens if you extract the juice from a few pounds
of duckweed and add this to your new aquarium? Or to a jar of aquarium
water set up on your window sill? (remember to set up one or more
without anything for a control comparison). What if you tried that 
with a variety of our aquatic plants? Might we discover a secret algae
inhibiting extract? Has this thought occurred to the folks at Tropica,
Tetra or Dupla I wonder? I would be most interested to learn the
results of any experiments along these lines, negative or positive.
I wouldn't be surprised to learn that certain plants were especially
good at this (such as Valisneria, Salvinia or Duckweed)

Another thought that occurs to me is that some plants might be much
better off in aquariums devoted exclusively to their own species.
I have read this advise in connection with Aponogeton madagascariensis
in various wordings. Some advise keeping other plants well away while
I think one article advised only growing the one species in the tank.
I wish I could afford to dedicate a tank to these lovely plants!!
You'd need a fortune to have enough plants to fill the tank. :-)

BTW, in a previous posting, George was only half kidding when he
teasingly asked me how I trained my otocinclus to eat green spot
algae. The way to train all algae eating fish to like eating algae
is to not feed them anything except what grows in the tank. It
sounds extreme but the fish are fine. I have heard of tanks of fish
where the fish were fed nothing at all except algae generated by
being in sunlight. I've been watching the Flying Foxes to see what
they like to nibble on. I've seen them tasting the green hair algae
(looks like green cotton fuzz) and nibbling at brush algae on a 
piece of slate but not really with much appetite. I've also seen
one use a kind of rasping, sucking action on a leaf but I can't
see the mouth clearly enough to see how the teeth are arranged. 
This fish seems extremely shy and easily disturbed from his feeding.
I've also seen Platys chewing on brush algae when they are hungry.

 - Steve