[APD] Re: theory behind algae control

["Steve Pushak" <teban at powersonic_bc.ca>]

The notion that providing nutrients in abundance to encourage macrophyte
growth has some validity but we need to remember that "algae" can arise
under many different circumstances. Green water flourishes for example,
when ammonia is present in the water & there are sufficient other
nutrients available & light is abundant. Macrophytes are better able to
utilize nitrogen in nitrate form than unicellular algae so using nitrate
instead of ammonia greatly reduces green water, in my experience &
according to others.

The cause for blue-green algae, or cyanobacteria, seems to be an
abundance of dissolved organic phosphates & perhaps other dissolved
organic nutrients together with moderate to high lighting. Adding
mineral nitrogen or phosphate does not seem to rectify this problem.
Reducing the light intensity to low greatly reduces BGA as does removing
the sources of organic nutrients (the fish & their food). I'm speaking
from my own experiences here taking into consideration how Tom has
explained BGA. I stress that these are empirical observations based upon
what I've done so far to resolve my own problems with BGA in a couple of
tanks. In one, I eliminated sunlight entering a tank & in my other, I
removed the pair of Bettas which needed to be fed a high protein diet. A
short period of blackout seems to have eliminated the remnants of BGA;
once you have it you need to remove the cause, remove as much BGA as you
can & kill off the rest.

The third broad category of algae is filament algae which you can
further divide into epiphytic algae (attached) & thread algae (for lack
of a better term, non-epiphytic?). As Tom has said, epiphytic algae does
seem not to attach to actively growing plants new leaves. I can't give a
compelling explanation other than to suggest that when things are
growing well, and dissolved organic nutrients are low, perhaps epiphytic
algae does not go into its reproductive stage where it has mobile bits
that float around & reattach to new surfaces. I suspect that a healthy
leaf also has some type of defence adaptation (a smooth surface?) that
makes it difficult for epiphytic algae to attach to. A damaged or old
leaf will always collect epiphytic algae. If you just remove any leaves
with epiphytic algae, it seems to be able to cure the problem. I suspect
that the algae is not really gone, but can easily reoccur if an
imbalance of nutrients tips the scales in favour of reproduction of that
type of algae. This is related to the "stability" explanation given by
Roger & Tom.

In my experience, non-epiphytic thread algae can flourish under any
circumstances where macrophytes can flourish. The competition
explanation might work here if you consider competition for light. A
tank of flourishing plants can quickly fill a tank very completely. The
filament algae at the bottom of the tank gets much less light & stops
growing as quickly. If the light level gets low enough, I suspect it
might die off after several weeks. Any filament algae which is growing
near the surface will continue to flourish. It tends to grow into a big
blob so what I do is pick it out with my fingers. I try to also remove
any fine leaved plants which have the filament algae trapped in the
leaves. If you do this religiously, sometimes you can get the filament
algae under control. A strategy of also reducing phosphates in the water
by encouraging macrophyte growth to take up those phosphates seems to
help a little. Again, I don't think the algae ever goes away; its still
present somewhere in the tank & ready to reoccur when an excess of
nutrients occurs; the algae is opportunistic & grows faster than the
macrophytes during periods of abundant nutrients.

You can't really help having BGA or green water in a tank because these
algae are so easily introduced by spores however, I firmly believe (you
need a certain amount of faith), that you can avoid filament algae if
you follow scrupulous quarantine & disinfectant procedures using bleach
to decontaminate new plants & quarantining fish for a couple of weeks in
a dark tank before introduction to planted tank. Once you have an
filament algae infected tank, its difficult to avoid
cross-contamination. Its also difficult to bleach sterilize fine leaved
plants unless you have the luxury of sterile & clean tanks that have
room & plenty of nutrients, light & CO2 ready to help the sterilized
specimens recover from their bleach trauma. Floating the sterilized
specimens seems to be the best approach until they are recovered enough
& large enough to plant.

I've also said that I think you will have a lot fewer problems with
algae of all kinds if you reduce the lighting levels to about half of
the "recommended" 2-3 wpg intensity. With good reflectors, I think you
can get by with about 1 wpg, and keep most macrophytes growing slowly.
You probably can't achieve the really high leaf area ratios as you can
in a strongly lit tank but you don't need really dense plant growth to
have an aesthetic tank, provided that you aren't loosing the lower
leaves on stem plants due to over shading. So a tank with primarily
crown plants (Anubias, Crypts, Swords) can flourish in a low light tank
more easily than a tank with a dense stand of Rotala macrandra.

It is an excellent question; we need to move beyond anthropomorphic
explanations. In my mind, there is always a competition factor. Growth
of an algae species will occur unless something it needs is not present.
Think about light competition in a succession environment where one
species out-grows another.

Steve P in Vancouver

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