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Re: comments on water analysis
On Sun, 6 Jun 1999, Hugo Hoekstra wrote:
Sorry, but this got long.
> >Gee. I wrote a response to this that should have shown up in APD V3 #1071
> >but it didn't show up. I'll try again.
> I also had that problem this week. Did you send the message under another
> alias than the one to which your digest is mailed?
No, but that can cause problems. The list software uses your return
address (correct me if I'm wrong, List Mom) to recognize you as a list
member and you have to be a recognized list member to post. If your
letter doesn't carry the name and email address you registered with then
the list software will bounce your mail into Cynthia's mail box where
further attention is constrained by the time she has avialable to look at
it. In all likelihood I caused by own problem by pushing the wrong button
or something because everything else in the path between here and the
digest is automated.
> >Actually, with regular water changes your 0.02 mg/l of iron might be
> >sufficient. Most things seem fairly well balanced, but if your plants
> I'm very happy with that, I'll add no more fertilizer just change 25% of
> the water every week or more frequent.
It makes aquarium care more enjoyable when you don't have to worry about
every little detail. My opinion, of course. Some people seem to like it
the other way around.
I have very little iron in my tap water, yet some of my tanks have gone
years without regular iron supplements and still grow healthy plants. Your
results will of course vary. These days when I do supplement iron I'm
using Beverly Ehrlebacher's suggestion and pushing bits of iron gluconate
tablets (from the grocery store) into the substrate below the plants that
seem to need it, when they seem to need it. That isn't often.
> >In looking at a water analysis like this, always remember that maintaining
> >fish in the aquarium always adds substantial amounts of nutrients to the
> >tank. The nutrients in the analysis aren't all the nutrients that you're
> >supplying to the tank.
> I know but when the necessary trace elements aren't being added through
> water changes or fertilizer plants will show defficiencies or not? I mean
> are fish providing any other nutrients for plants than ammonia, nitrate and
> nitrogen ?
Keeping and feeding fish in a planted tank should provide most or all
of the minor and trace elements need by plants. But some explanation
seems to be called for.
There are something like 21 different nutrient elements that are essential
to plants. Prepared fish foods probably contain all of them, but the
nutrients don't start out in a form readily available to plants.
Phosphorus is found in bone, phospholipids and nucleotides and the other
elements are found mostly in proteins. Potassium, magnesium, and calcium
are present at least partly in water soluble forms and they might be lost
from the dry prepoared foods.
Live fish foods and fresh vegetable foods contain the same elements in
much the same forms as prepared food. It might be necessary to feed a
wide variety of live and fresh foods to make sure that all of the
necessary nutrients are present.
From aquacultural data (liberally interpreted to aquaria) the fish
probably metabolize 60 to 80 percent of the food they're fed. The rest is
either uneaten or eaten and passed. Some of the nutrients in the 60 to 80
percent that is metabolized is stored in the fish (in growing muscle and
so on). Most of it is used for calories and for maintenance of tissues.
In the case of foods burned for calories or used for maintenance the fish
don't (on net) retain the nutrient elements. They excrete amounts equal to
what they eat. The excreted elements are generally more available to
plants than they were in the original food and some of the nutrients may
be completely mineralized to plant available forms.
Unmetabolized foods and nutrients excreted in forms that aren't available
to plants have to be further processed by microbes in the tank before they
become available to plants.
Once the nutrients are released in plant-available form they don't
necessarily stay in that form. The same is true of nutrients added in
trace element mixes. Metals especially tend to form complexes and solids.
In those forms the nutrients may not be as easily taken in by plants.
Fortunately most of those metals (micronutrients like nickle and copper,
for instance) are needed in extremely small amounts and are almost always
So I can see four possible problems with using fish feeding as your main
source for plant nutrients.
First, the feeding rates have to be high enough to balance the plant
growth rates; if you don't have fish or if you have too few fish then it
won't work well.
Second, water soluble elements like potassium, magnesium and calcium may
not be provided in large enough amounts to supply the plants; those need
to be provided by water changes and supplements.
Third, the balance of nutrients may not be exactly what the plants need;
this is mostly a problem with elements that are needed in fairly large
quantities like nitrogen or iron and if shortages arise then supplements
are called for.
Fourth and finally, the whole process works better in mature tanks with
established and diverse microbe communities for mineralizing the
nutrients; new tanks may need nutrient supplements that are unnecessary in
Feeding and in-tank metabolism also provides CO2, but CO2 is readily lost
from the aquarium so I haven't included it in my thoughts. Generally if
you want a large variety of healthy and attractive plants with moderate or
high growth rates in heavily planted tanks then you need to supplement
If you do encounter a possible nutrient shortage or imbalance, keep in
mind that you may be able to avoid the problem by reducing the lighting
level in the tank, thus decreasing the growth rate and decreasing the
plants' demand for nutrients.
> And I do have a new question, are there any factors which can *raise*
> the pH in a tank besides certain rocks?
Raising pH isn't usually a problem. Use the pH-KH-CO2 relationship to
manipulate the pH. To increase pH you can either increase KH (adding
rocks) or decrease the CO2. Decreasing CO2 means either adding less or