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Re: Algae experiment

> I know levels of N and P slightly above zero are recommended.

What's "slighty above zero" mean? 5ppm? 1ppm?

> I've
> intentionally driven nitrate and phosphate to near zero levels in a
> high-input 90 gallon tank. Lots of CO2, light, K and trace supplementation.
> Most of the substrate is covered with sword plants and I assume that those
> plants draw most of their needs from the substrate (laterite and gravel with
> added fertilizers). The back and sides of the tank are covered with black
> eggcrate, the upper half of which is planted in hygrophilia difformis, the
> bottom half in the shade is planted in anubias coffeefolia. All the plants
> are growing well so far. Since it is totally water borne in this tank, I
> expect the difformis to stall out as N and P levels continue to drop. I'm
> going to try to add N and P only through fish food. Algae is minimal except
> for a form of green spot that is more like green dust.

Well since your plants are slowed(due to lack of N), try backing off the
traces(say weekly instead of once every 2-3 days or daily etc).

> It is a very rapid
> grower and easily comes loose into the water. The question is, how is this
> algae able to keep going with nothing in the water to support it?

Oh there's plenty in the water. Most algae have extremely low needs for both
N or P. These needs are below the resolution of our kits in most cases. Fish
waste, rotifer waste, possible plant leakages from being stressed, all
contribute to this. They have incredible storage capabilities.

The amount of biomass produced relative to their needs is huge. It simply
does not take much "food" to make a nasty presence for many algae species.
They are water column specialist, your not going to starve them to death as
you will find out. Your plants will die first. They are much much larger and
need far more "food" than algae. Algae are very well adapted to the water,
plants are "late comers" perhaps even being the "lower" group .......at
least in the water.
> BTW, the rotala macrandra really hates these water parameters, even though
> it is rooted in the substrate, so I guess that speaks to the need to keep N
> and P above zero for some plants.

So basically you've answered it for yourself, you cannot out starve the
algae........without causing harm to your plant.

Now try this approach on a non CO2 tank with lower lighting(say 2 w/gal).
Don't added any traces to the water column(particularly iron).
It's plausible to "limit" a number of algae in that system. But the system
is also CO2 "limited". So is it iron limited or CO2 limited then? You have
an interaction there. Growth rates of algae are slower in these types of
tanks. Algae can still use HCO3 for Carbon source(some plants too), some
floating plants weasel around this also.
If you add CO2 to  a low light tank you get nice growth and nice colors and
low algae presence also. You don't get the nicer denser growth of a number
of plant species though.

As lighting and growth rates get in the 2-3 watt/gallon range and with
adding CO2, substrate transport rates are simply to slow to keep up with
plant growth and you need to add traces through the leaves also. At these
lighting values you have to add traces to the water column for most plants
otherwise the growth rates will stunt the plant's reserves and slow
growth/reduce plant health overall. Not good.

You can also remove all of the substrate's contribution to the plant by
adding nothing to gravel(use plain sand) and use a UG or RFUG filter and add
all the nutrients to the water column. Then the roots are not taking in much
relative to the leaves. Some uptake will be present since the bacterial
films will be contributing and roots use chemicals to sequester some
nutrients. There are other concerns here but let's keep it simple:!)

Water changes remove allelochemcials, rotifers, suspended algae spores etc.
That keeps things simpler too.

UV's may also help for these issues also by breaking down allelochemcials,
killing rotifers, algae spores, there by increasing light penetration also.

You can try the CO2 vs the non CO2 thing for fun and excitement:) There's a
lot to be said for the non CO2 system. But that CO2 is a drug.......

Tom Barr 


> Tom