Re: Freshwater Plenum???

>From: James Purchase <jpp at inforamp_net>
>With all the attention currently being paid to the use of plenums
>(water-filled space underneath gravel bed) in Marine tanks, has anyone
>ever thought of possibly using the same technique in a Freshwater plant

Plenums under plant tanks have been discussed, but in my estimation, the most
useful aspect of one of these would be if it gives you the ability to inject
and diffuse nutrients below the substrate where the plants can get to them
before algae.  

>Would anyone care to comment on why it would or would not work to keep
>nitrates down in a freshwater environment as it seems to do so in

If you plan on a lightly planted tank that won't have problems with phosphate,
or a heavily planted, but also heavily stocked aquarium, a plenum may help out.
I still haven't heard anything about whether there is a reduction of phosphate
that occurs at a certain redox level.  My guess is that there isn't, so
phosphates still remain the biggest problem in a lot of cases.

Healthy plants themselves will consume first ammonium, then nitrites, and
finally nitrates (some plants probably can only consume ammonium, but the
majority can probably consume all three).  If you have a tank that's nitrate
levels increase despite the plants, you'll probably need to also keep an eye on
phosphates.  IMO, phosphates are a bigger contributor to algae problems than
nitrates.  The nitrate concentration only dictates which algae grows the best
when the phosphates are too high.

I probably didn't answer your question very well.  Since plant tanks often have
a relatively deep substrate, it's not uncommon for reduction to occur in the
substrate.  As it stands, the use of a plenum in a marine tank appears to be an
experimental procedure aimed at diffusing H2S so that pockets don't develop
which can erupt to the surface with potentially deadly reusults for the fish.  

I don't really know if a plenum would be helpful for limiting H2S production in
a a plant tank.  A mature plant tank will probably have leftover, dead root
structures from uprootings that will decompose in the substrate, potentially
requiring the reduction of SO4-- ions to supply oxygen for the bacteria.  One
thing different about a plant tank than a marine tank though, is the presence
of root structures that often permeate the entire substrate, supplying oxygen
everywhere.  In order to make the plenum useful in this context, I'd suspect
the substrate would need to be very deep.

Anyways, just my thoughts.

David Webb in Plano, TX.