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Re: Tanks Surviving in Arizona
Jason Smith wrote:
<Regarding the plenum>
> 1. incomplete denitrification (due to lack of sufficiently anoxic areas in
> the substrate (perhaps caused by increased water movement through the
> substrate from substrate heating/higher temps in general??)) will generate
> nitrate levels that can only be removed by water changes
Anoxic conditions and subsequent denitrification are caused by bacteria
feeding on organic detritus in the substrate. The plenum plays no role
in either process. In fact, the plenum doesn't even provide habitat for
the bacteria, as they live on surfaces -- mostly in the substrate -- not
in open space. After long consideration, some experiments and
discussions with reef keepers who did the same I concluded that the
plenum does nothing but moderate anaerobic conditions; it doesn't create
them or even promote their existence.
The Jaubert method in reef tanks used live sand over the plenum. I
talked with one reef keeper who experimented extensively with the
Jaubert method. He concluded that any observable effect was created by
the live sand cycling organic nitrogen, not by denitrification and not
by the plenum. A plenum would help keep conditions from becoming too
anoxic to support live sand, so live sand with a plenum worked better
than live sand without one.
Keep your plants healthy, well-lit and moderately fertilized (especially
with CO2) and don't over feed your tanks. Your plants will grow quickly
enough to use as much nitrogen as you add with the fish food and you
will never need to change water because of nitrate buildup. You may
have to change water for other reasons.
> 2. gradual increases in hardness due to evaporation/"topping off" will
> lead to non-optimal conditions/metal toxicity. Again, from my reading,
> these two points (nitrates/hardness) are the reasons some advocate weekly
> water changes (something I would like to avoid or at least delay). My
> understanding (limited as it is) of plenums/Jau... is that the anoxic
> areas created will slow/prevent/reverse? some of the oxidation of metals
> that make them unavailable to plants.
Well, there's a couple things here.
First, water in the west (except the northwest) usually contains a lot
of minerals. There's probably no way to get away from a long term
buildup of minerals in the aquarium. It happens. You can keep it from
building up faster than necessary by using RO, DI or distilled water for
makeup and by minimizing the amount of chemicals you add to the tank.
You don't need to worry much about that for your plants' sake, as most
can take a wide range of mineral content. Fish are pickier, but not as
picky as some people think.
I don't know of any metal that's likely to build to toxic levels through
evaporation in an aquarium. Most common metals form benign or insoluble
compounds under oxidizing conditions -- and especially in well-buffered
water. Our aquarium water is generally well oxygenated, so metals fall
out of solution or get "detoxified" over time.
Soil substrates may provide conditions where metals can reach toxic
levels. See Diana Walstad's book for more information. I think that
metal toxicity problems are more likely to be associated with low pH
than they are with any other factor.
> > Umm... Methods for what? If you mean general plant tank methods there
> Sorry, I was unclear. I was specifically referring to methods that require
> infrequent water changes/dilution. I'm already planning on the "obvious?":
> dense plantings, very light fish load, CO_2 injection...
That should do it.
> As to the water use (which is really the point to all of this I guess), I
> feel guilty in PA dumping the extra 10 or so gallons, though as you say,
> in the grand scheme of water use its not that much. I would just like to
> minimize whatever waste I can.
Then you will probably find conditions in the west to be very
frustrating. The massive waste and hypocrisy in public policy is