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Plants do NOT use NO2

>> Plants are lazy, so they will take the more reactive
>> ammonium and nitrite forms of nitrogen more readily than
>> they will use nitrates.

This is 1/2 correct. NO2 is highly toxic to plants internally. They will NOT
take in NO2. It is very quickly converted in the cytosol at the surface of
the chloroplast from NO3-> N02 -> NH4+. NO2 is the one N species that will
persist in a new tank. NH4 is used fast as is the NO3. Many seem to think
that NH4 is preferred exclusively. This is not true. Plants DO prefer a
balanced ratio of NH4 to NO3. It just takes a bit more energy to use some
extra NO3 to make up for the NH4 but the plants main source of N is still
NO3. This optimum ratio is about 4 NO3:1 NH4. Now if you consider toxic
levels of NO3(they are quite high) and toxic levels of NH4 (these are quite
low) every tank will be low on this ratio for NH4. This doesn't mean that
your tank will do poorly but it does lend a good reason to have snails,
fish, shrimps etc since they produce NH4 in small trace amounts that dole
out small levels to the plants. Adding a big flux of NH4 on the other hand
is not a good idea, unless you like dead fish. Ammonium is pretty toxic and
a good way to increase algae. You don't want a lot. So this leaves us with
NO3. Some substrates have higher levels of NH4+(say if they have
peat/organic/soil based substrates) that plant roots will use. It can be a
problem if you uproot things too much at once.

>That has a powerful
>> water-cleansing effect on the more toxic forms of nitrogen
>> compounds. As the plants photosynthesize, they give off
>> copious amounts of oxygen, which further eases any fish
>> with slightly burned gills.

Again NO2 is not used by plants except when they convert NO3->NO2->NH4
(NO2->NH4 this IS the fast step in this assimilation process).
NH4 can burn the gills. You can look up levels that are toxic for fish on
the web(there's some in the archives also).
> For some reason, I thought that the plants just absorbed the
> nitrates... 

They can and do.

>> Fish (and to a great extent plants) do not feel pH and
>> don't really care about it as a condition for happy life.
>> pH shock and a lot of other mythology developed around a
>> lack of understanding of the chemical effects of pH,
>> particularly with ammonia and nitrites.
> Really?! I've been thinking (and reading...) that fish were
> very sensitive to ph swings. I've been thinking to start
> injecting CO2 into my tank with a homebrew CO2 setup, but I
> have been very hesitant to do so because I was concerned
> about the effect the pH swing would have on my treasured
> fish.

Not with your water. Use only CO2 gas to get a pH of 6.9 target(6.8-7.0
range). Plants and fish do care to some extent the pH, as it relates to CO2
levels. If is a slow change it can be tolerated also. Abrupt changes are not
>> Tank "cycling" has its own fish-store mythology. A growing
>> tank of plants never cycles, as the plants quickly steal
>> all the ammonium from the bacteria. It can be stable from
>> day 2. 

Well it does cycle you just don't see it(able to measure it). With the
plants the cycling goes unnoticed from their uptake. Plant tanks will eat
all the ammonium up if heavily planted from the start. No NO2. Too many
people are cheap, do not get enough healthy plants when they set a plant
tank up and think it will simply "grow in". It can but it is so much better
to add plants than remove algae later. An extra few dollars spent on plants
is well worth it when starting a tank out. Perhaps some of the best invested
dollars in the hobby is buying enough plants.

> Wow! This is counter to almost everything I've read
> concerning keeping fish! I wish I had come across the APD
> when I first started keeping fish (about a year ago)... At
> that time, I just got plastic plants thinking that real ones
> would be too much work for the benefit they provide. I had
> read that real plants would be beneficial, but I just wasn't
> convinced that they would make all that much of a
> difference... 

The roots also add O2 to the gravel which also helps bacteria there grow
much better. But the plant roots also have bacteria on them that help cycle
a tank very well. 

Adding the old filthy mulm from another established tank is one of the best
ways or an old mature filter. I add old mulm when I set up a new tank. I
vacuum out about 5-10 gallons of gravel vacuumed water and let it settle for
a hour then decant off the clear water saving the mulm on the bottom. I add
this and some ground peat to very bottom of the gravel layer. I add
SeaChem's onyx over this. I save a touch of the mulm and seed the filter
with it. Do that with heavy planting from the start and you'll be very
happy. Add algae eaters (SAE's then shrimp) after that(one two days).

Hope this helps!
Tom Barr  

> T(itus). =8)