scs0 wrote:
snip
My colorcoded water test strip shows that my nitrite level is over 1
which is considered safe, but I did read that long-term exposure to
elivated levels can be harmful too. Most of my submerged vegetation
either died off in the winter or was eaten by my fish so if more
plants will suck in the nitrites I'd like to stock up.

I consider 1ppm nitrite to be right on the edge of 'bad news'. Nitrite
poisoning is a nasty thing. If nitrite is taken up into the fishes'
bodies, it will bond with hemoglobin in the blood, creating a form that is
unable to transport oxygen. If too much hemoglobin gets thusly converted,
the fish essentially suffocate to death because their blood is unable to
transport sufficient oxygen. The signs this is getting serious is when
they are gasping at the surface or gathering in oxygen rich areas. Given
than your fish are displaying such symptoms, I would think you're very
close to the critical threshold.

Now, in a normal tank I would add rock salt to mitigate the effects of
nitrite poisoining after doing a water change. The chloride ions in salt
compete with nitrite in the gills for uptake. If you have sufficient
chloride ions (usually as little as a teaspoon per 20 gallons is enough in
this case), they will be absorbed instead of nitrite. Water changes of
course reduce the nitrite concentration. How this would translate over to
a pond situation, I can't quite say, having never added salt to a pond.
You should however think about doing a water change to get some fresh
water in there. Also check for (and remove) any sources of nitrogen such
as decaying plant or food matter.

As for plants, I did a study for plant bio classes years ago using
terrestrial plants. There were three groups fed ammonia, nitrite and
nitrate as their nitrogen sources. Those fed nitrite were the worst in
terms of growth. Most plants prefer ammonia and nitrate as a nitrogen
source. They will use nitrite, but it is not preferred. Now, on the flip
side, adding plants might help by absorbing enough ammonia before the
bacteria converts it into nitrite, thus indirectly reducing the nitrite
levels. Plus, removing nitrates will help allieviate some of the stress on
the fish. Just make sure they are healthy plants that won't decay and add
to the problem. Also make sure you don't add so many plants that they
compete with the fish for oxygen at night. Right now you also want to
focus on keeping the water well-oxygenated so the fish can get sufficient
oxygen even with the nitrite poisoning going on. Perhaps focus on
oxygenating plants for the moment and replace other plants later on.