Re: Plants competing with algae

George wrote:
> I think all of us at one time or another have stated that it's good to
> densely plant because "plants outcompete algae for nutrients".
> I've always felt uncomfortable about this.  Does anybody know the
> basis of this statement?  Can plants use nutrients faster, thus
> removing them from the water before algae can use them?  This seems a
> little far fetched.  Nutrients should be evenly distributed in the
> water column, easily usable by anything nearby.  
> I prefer the "allelochemcal" reasoning for dense planting.

I think the important thing here is that when a tank is first set up
for plants esp. if it has had fish first and light is increased,
conditions are perfect for algae to flourish because there is such
a high concentration of nitrates, phosphates and ammonia. The main
thing is to prevent the algae from getting started because once
growing, it spreads. Algae is opportunistic and will bloom whenever
there are good conditions. I'd like to believe that allelochemicals
are effective at slowing the growth of some algaes but even dense
planting does not seem to inhibit brush algae much. It does slow
with increased CO2 bringing the pH below 7 to around 6.5 - 6.8.
That's another reason I'm not adding any carbonates in my tank. I
want the pH in that range even if it means a larger pH change if
the CO2 fluctuates. I've not had a reoccurence of green water since
I've gotten better growth with CO2 injection. I attribute that to
the denser planting. Once the majority of brush algae growths
have been removed, I think it can reasonably be controlled by
a combination of pH, allelochemicals from dense planting, and
algae eating fish and snails. I don't think of this algae as
one which grows as rapidly as green water algae or blue-green 
slime in opportunistic situations.

Look at it another way: a new tank with no visible algae is
setup, gravel added, fish added, lots of plants added. Initially
there is just ordinary tap water. We continue feeding and the
fish excrete producing ammonia etc. If the plants metabolize
the nutrients efficiently the nutrient levels never get high
enough for the rapid algae growth to occur. Algae reproduction
is limited by the lower nutrient concentrations and allelo-
chemicals. (what the heck; why not both?)

This would imply that a brand new tank with new gravel should
have fewer algae problems than an existing fish tank which
has introduced plants and increased lighting. The difference
would be the initial concentrations of nutrients. I have a
feeling that many experienced plant people prefer to start
with fish first rather than from clean? (contrary to this)

To return to the statement "plants outcompete algae for nutrients",
I think this is slightly inaccurate. I think it is important to
keep nutrient levels at controlled levels or else the algae will
flourish because it can reproduce and grow much faster than plants.
I think the allelochemicals are very effective against some
algaes and partially effective against others. I remember hearing
once that green water algae really inhibits brush algae. Anybody
agree or disagree with that rumor? I'm definitely not saying its
so. (Maybe I'm just starting up a new myth ;-) I don't think 
dense planting or anything except algae consumers is going to
eliminate algae that is already present. You have to remove it.
You cannot starve algae to death.