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Re: NO3 and some resolve

On Mon, 11 Jun 2001, Jay Reeves wrote:

> A couple of weeks ago I measured nitrate a day or two after a water
> change.  The test indicated elevated levels that were not consistent
> with recent experience. Ah ha!  forgot to turn the Magnum back on after
> the water change.  Turned the filter on and the next day N levels were
> back to normal.

Jay, it's possible that what you observed isn't related to biological
activity in the filter.

Are the plants in your tank mostly dependent on foliar intake for their
nitrogen supply?  If so, then the poor circulation while the pump was off
may have cut the plants off from their nitrogen supply.  Without
circulation, the plants deplete the nutrients in the water bordering the
leaves, but they can't get to the nutrients (nitrate in this case) that
are farther away from the leaf.  Nitrification would continue, as the
nitrifying bacteria are free to break off from surfaces and live freely in
open water.  Even if you don't add extra nitrate, nitrate could continue
to build up in the tank and the plants would just strangle (figuratively)
on the nitrogen-depleted water next to their leaves.

When you turned the filter back on and re-established the current the
plants suddenly got their nitrogen supply back and probably took it in at
an increased rate to make up for the few days that they were deficient.
Nitrate levels dropped as a result of the accelerated uptake.

Or the nitrate could have dropped because of denitrifying bacteria in your
filter.  If that is the case then you can see this as a good thing or a
bad thing.  If you're adding nitrate to keep the plants happy, then it's a
bad thing.  If your counting on your plants to control the nitrate
produced from fish waste and fish food then it would be a good thing and
give you a margin of safety.

As Tom and I both pointed out, denitrification isn't an easy thing to get
going at significant rates, and cases where denitrification appears to be
important are rare.  So I think it's more probable that the rise and fall
in your nitrate levels was caused by shutting the circulation off and on,
not by the bacterial action in your filter.

Roger Miller