Re: mixing powders & substrate vs. dissolved nutrients

I wouldn't mix powders together. Absolute precision in the
ratios of the ingredients is not critical. In most cases
you will be measuring things by the teaspoon and that is
quite accurate enough especially if you take care to level
the powders off in the tsp. or tablespoon.

I wouldn't mix very much nutrient mix up in advance either.
PMDD nutrients are fertile for growing all sorts of things
such as fungus. Keep it stored in the fridge. Some kinds of
chelated metals can be displaced slowly by other ions in
the solution and would then be precipitated.

I'd also like to bring up another subject which people don't
seem to understand about fertilizing chelated iron in the
water of aquariums. An aquarium (with fish) typically has
a great abundance of N & P many times higher than are found
in nature. With strong light, if there is sufficient iron
in the water, this can lead to an explosive green algae
bloom. The reason why we often need to add chelated Fe is
because our substrates are often horribly deficient of Fe.

In reviewing old issues of TAG, I discovered data which
documents the tremendous amounts of Fe which are available
in virtually ALL mineral soils. Only gravel due to its
low surface to volume ratio and sand really have low Fe
availability. In fact, according to the article some lateritic
soils contain as much as 300 mg/g of Fe. This is 30% Fe
atoms by weight! Soils low in organic content (ie mineral
soils as mentioned in dr dave's recent posting) are also
very rich in micro-nutrient minerals.

A certain amount of organic material is necessary in a
substrate to fuel bacterial activity which can lower the
redox potential in the substrate (so-called anaerobic
or anoxic condition) which permits _bacteria_ to make
mineral nutrients like iron available to the plant roots.

Studies have shown that approximately 5% organic material
are the optimum in substrates. In an aquarium, this 
should probably be organic material which has already
almost completely undergone decomposition. Raw manures
etc. are very labile (subject to decomposition) and can 
place excessive oxygen demands and this can even affect 
your fish. Labile or fertile organic material or inorganic
fertilizers can decay in the substrate and liberate too
much nutrients early on.

There are ONLY three nutrients which we MUST ensure
are in solution in the aquarium. There are strategies
for supplying all others in the substrate. These
nutrients (req'd in solution) are: magnesium (Mg),
calcium (Ca) and potassium (K). With the PMDD method
unless you have sufficient Ca in your tap water, YOU
need to add some form of calcium. One tsp of calcium
carbonate for each 10 gals of water changed will probably
be quite sufficient and supply adequate carbonate for
CO2 injection for very soft water. You may choose to
increase carbonate further to achieve a pH and CO2
concentration for tuning.

OTOH, if you are growing floating plants or green water
algae in small tanks as a means to control water
conditions (ammonia and nitrite/nitrate) or to feed
daphnia, infusoria or other live foods, then the
addition of trace amounts of chelated Fe can be a
very good thing. A small amount of soil in the bottom
of a container will supply enough Fe to keep unrooted
plants alive and growing.

By golly, I seem to have drifted off my original topic (again).
Hope it's been informative! ;-) 

Steve   cruising the TAG back-issues again   :=)