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PO4 and Algae

An interesting thread on algae limitation by Roger back in February. See
APD 4#109,110,111. I think I'll vote for #2, the grazer theory. SAEs are
very good at keeping many kinds of filament algae in control provided
that there aren't huge amounts of it. Other kinds of fish will keep
Spirogyra in control but won't eat the slightly coarser kinds. Snails
help with this too but they don't seem able to control a high density of
it. In an environment with a surplus of minerals and no additions of
trace nutrients to the water, I observed diminished filament algae
growth rates until I added nitrogen. At this point, the algae growth
exploded. This correlates well with the suggestion by Karen that N is
very commonly the growth limiting nutrient. I believe that you can push
the system over into phosphate limited growth by adding nitrate
regularly but I think you need to have either: no filament algae present
in the environment (i.e. bleached) or some SAEs or similar algae
grazers. Which grazers you'll need depend upon the coarseness of the
algae and the abundance of alternative food supplies. If you don't have
the grazers, then you need to be persistent about removing the algae
from the tank until you've got the phosphate levels in control. Then you
need to have enough plant mass to rapidly absorb the phosphates being
released through feeding the fish. If you have soil in the tank,
depending upon the type of soil you used, it may take a long time for
the soil to stop releasing phosphates to the water. Remember, soil is a
big phosphate sponge, especially soil with humus in it. By that I mean
that it releases phosphates for a long time.

You might want to consider limiting nitrogen; you'll have slower
macrophyte growth rates and thus lower maintenance.

If you're using soil, you might want to try to choose a primarily
mineral soil such as subsoil or clay. You can use a little peat as peat
is very low in nutrients. Its even better if you use the soil in pots as
this is much easier to manage; just lift the whole pot out if you need
to remove a plant for sale, to remove cuttings or daughter plants.

The clay ball approach is also very effective if you have a regular
gravel substrate especially if you want to add plants to an old
established aquarium and you don't want to tear it down.

When you compare Diana's garden soil formula, keep in mind that I think
her tanks may have relatively lower lighting levels and may not always
be CO2 supplemented. Trying to adapt garden soil to high light and CO2
means, I think you need to have a good grazer crew especially if your
tank has filament algae populations. Filament algae is easy to spread
among tanks by nets or water changers especially Spirogyra!
Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!