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Re: aquatic composts

Steve Pushak wrote:

> Mix a shoe box of dirt with your compost (kitchen wastes work nicely)
> and let em compost for a few weeks, stirring occasionally. Once the
> composting has proceeded far enough, the microbes in the soil will have
> turned most of the carbohydrates into minerals which are safe to be used
> as plant food without producing a bacterial bloom. These minerals are
> extracted from the soil using water. (I'm simplifying the detailed
> procedures Paul [Krombholz] describes) You get a concentrated yellow 
liquid which is > very potent.

Mmmm.  Essence of compost.  Just a little dab behind the the ear and.... 
never mind.

This is a slightly different idea from my suggestion, because it uses
material from sources other than the aquarium.  On the other hand, this is
a valid idea.  I read of "compost tea" several years ago for fertilizing
house plants and starter plants.  I never thought of using it in an

My thoughts were actually more similar to waste water treatment processes
than to normal garden composting, because I want to use a high water content
and the process should work relatively quickly.  I think that fertilizer 
made from plants harvested on one weekend might be returned to the tank 
on the following weekend.


Neil Frank wrote:

> Adding large concentration of soluble phosphorus will be worse than adding
> N and probably result in an immediate algae bloom.

Cetainly this could be true for some tanks.  In my tanks I doubt that
phosphorus is a limiting nutrient, so additions of phosphorus aren't
necessarily a problem.  Also, the N:P ratio in plants is higher than in
most fish foods (I think I can attribute this bit to Diana Walstad), and
high N:P ratios mean that phosphorus should be limiting.  So if you
are keeping fish and you aren't adding nitrogen fertilizer (forcing N:P
high) then the tank probably now has a comparatively low N:P ratio.  Using
recycled plant material as a fertilizer isn't likely to cause any new

Whew! Logical gymnastics.

Still to be on the safe side it would be good to test the fertilizer for 
its phosphorus content. 
> >You could also put the soup into a media chamber in a filter.  That would
> >keep the detritivores and herbivores out of the picture and allow slower
> >breakdown, but you're still likely to get a big slug of nitrogen that you
> >don't want. 
> This will also add a big slug of P, right?

If the first instance is a problem then so is this.

> >
> >So how about taking the soup through a decomposition step outside the 
> >tank - the aquatic equivalent of compost pile?......   Some of the mineral
> nutrients 
> >will be in the water, and some will remain in the partly decomposed plant 
> >material.  
> Unless I am missing something, the P will still be in the water, right?

The P could be in the water, or it could end up in the solids.  I think 
in sewage treatement facilities that P tends to concentrate in the 
solids.  A plant operator, environmental engineer or anyone else who 
wants to pitch in can correct me on that.

> > ......  I think you could 
> >filter the solids and return a useful trace element mix to the tank.  The 
> >solids would be kept in the bucket until they reach a nice, stabilized 
> >form and then used for a substrate amendment.
> >
> It would be nice if you can remove the soluble phosphates. What about
> discarding the liquid part from the solid mush .... or adding soil (and/or
> small amount of iron sulfate) into your aquatic compost. The idea would be
> to form insoluble iron phosphate. Then figure out a way to get it into the
> substrate and out of the water column.

The ferrous sulfate idea is interesting.  I thought of using a phosphate
sponge, but that is relatively expensive and may not work so well in the
presence of the big organic load that the liquid would carry. 
Agricultural grade ferrous sulfate is cheap and some of the added iron
might get chelated and carried back to the tank. 

> - --Neil

Thank you both for the feedback.

I started a batch of this stuff with the trimmings from today.  I'm
aerating the "green soup" in the bottom of a 2-liter pop bottle.  So far
its turned black and it looks... well, it looks a lot like sewage.  I
figure I'll cycle the bubbles on a off for a few days, then check the
ammonia, nitrate, nitrite and phosphorus levels in the liquid.  A
practical process might need two steps, one anaerobic and one aerobic. 

Roger Miller