Re: fertilizers

Mike Taylor <MLT at juno_com> asked about commercial fertilizers....

I've been doing some research on substrates which is closely
related to methods using both solid and liquid fertilizers.
A soil substrate esp one enriched with manure can supply almost
all your fertilizer requirements including Fe. Eventually however
experience seems to show that the tank will become deficient in
some nutrients in particular Fe (sometimes) and almost certainly
K & N particularly in high lighting situations such as yours.
In situations like KB Koh where he has trouble locating chelated Fe
I'd encourage him to use soil substrate. You could enrich your
substrate with almost any Fe supplement or even fine steel wool
to create rust. Of course the PMDD recipe works very well but
you may need to boost the amount of nitrate and maybe the potassium
in a high light tank. If you're going to add fertilizer in
solution, don't use a commercial mixture. Buy the component
chemicals for PMDDs and start off with the dosages they recommend
but skip the trace element mix if you cannot find it.

To give your plants an advantage over algae, I think its better
to add solid fertilizer (as in Jobe's plant food spikes) after
about a year of using a soil substrate (depending upon how much
N-P-K was there to begin with as manure, enriched soil or initial
fertilizer). This puts these important macro nutrients in the soil,
not in the water where the algae can _rapidly_ utilize it.
Within reason, the more N-P-K is available, the more growth you
will have. That brings us to the problem of algae control. If
you have a rich substrate, it doesn't pay to disturb it greatly
as you risk a green algae bloom. Also the plant material in a
tank is always growing and some of it is dying and decomposing.
You're also adding fish food. The fish food, fish excrement and
decaying plant material all release lots of macro nutrients 
right back into the water. The problem is the phosphates. Too
high a concentration and BLOOM: green water! There is usually
an excess of phosphates probably accumulating from the inputs
of fish food.  Fortunately in a tank with actively growing 
plants, they absorb those nutrients just as fast as they 
are being released provided that they have enough Nitrogen 
and Potassium to maintain the growth (not forgetting
all the other important factors we keep mentioning here: light,
CO2, trace nutrients) I've found that if you remove too much
of the actively growing plant material, the balance can be
disturbed. There are two effective strategies for dealing with
the green water: 1) in advance ensure that you don't become
N-K deficient and use at least one very fast growing plant
such as Salvinia 2) use a diatom filter to remove the suspended
algae. This works well because it removes those excess nutrients
which have been captured in the bio-mass of the algae
at the same time. Using a combination of Salvinia and PMDD
supplements I have almost licked a bad green algae bloom without
resorting to filtration. It works.

I hope to have some really interesting material to share on
substrates in a while; I'm working hard to understand the scientific
data. As for the acidic water problem and the possible copper/lead,
I'm planning to get on the water supply utility for data and get
a Cu test kit to see how bad it is. Sounds like carbon filtration
may be a potential answer but where to put a holding tank? Karen,
any clue as to when you expect problems with acidity and resultant
high Cu? Yes, the snails have disappeared from the tank I did the
recent large water change on. Fortunately I have a small breeding
tank full of Betta fry that's chock full of them and I can
restock. ;-)

Steve in acidic Vancouver BC