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Re: R.macrandra, H. polyperma and tank conditions

Re: Rotal macrandra, Karen says
>Maybe that has something to do with my better luck with the plant.  My
>water is moderately hard.  I do find that I need to keep it planted in
>soil, and it must have supplemental CO2 to grow under my tap water
>conditions.  I have always assumed that it also needed high light, just
>because the tanks that I grow it in (which are the ones with supplemental
>CO2) happen to have strong light.  Of course, Neil has gotten me thinking
>now, and I'm planning on putting some in a tank that has supplemental CO2
>and soil, but LOWER light, so that I can see if the light is a necessary
>part of the equation or not.  

What Karen's comments point out is that the COMPLICATED "equation" includes
concentration of many chemicals both in the substrate and water (inorganic
and/or organic) , in addition to lighting (intensity, duration and color)
and other factors. All variables must be jointly considered when drawing a
conclusion. I can grow R. macrandra with only 80w over a 70g  (~280L)tank.
The tank has many other plants, including Echinodorus tenellus,
H.polysperma, many crypts.. and all are doing fine. This tank only gets a
little over 1 watt per gallon!! My water is soft and has low alkalinity.
Her's is harder (both GH and KH). My low light tank has peat in the
substrate. For many years this tank supported macrandra without much effort
- no added CO2, only occassional additions of trace elements (except for the
regular water changes which DOES add stuff), but it grew slowly. Recently I
added CO2, and the macrandra and some of the other plants went crazy....
Karen and I were literally watching them grow. Now the CO2 system is under
control and providing a more steady amount, the plants are growing even
faster.  Still with 80w. (When I have time I would love to see what happens
when I increase the light... the tank already has 2 extra bulbs in position,
and all I need to do is flip a switch).  In other tanks with the same tap
water, I needed CO2 to get macrandra to grow with soil substrates and low
light.... In my water conditions, I think the peat was supplying something
extra... probably CO2 and maybe more. Karen has been using soil (I don't
think she has tried peat (yet <g>), and she has uses CO2 and more light. 

In general, the "chemicals" we think about include nutrients, CO2, various
organics, as well as the  potentially inhibiting allelopathic compounds.
Minimum amounts of nutrients and CO2 are what we 'normally' consider for
good growth. The _combinations_ and the relative balance may also be (is)
important. One part of the equation may be the GH and KH. And this may be an
oversimplification, because the higher levels of Ca vs. Mg may have
different effects. The same may be true for higher concentrations of ions
from other 'salts' (Cl, SO4, or whatever else is associated with 'hard
water'), as well as high concentrations of the trace metals. Some of these
can interfere with (block) the plants ability to utilize the available
nutrients, right? 

One set of plant responses take place at so-called typical water chemistry,
but other things seem to happen at lower and higher levels of various
chemicals.  Copper and other metals are another wild card, and Karen's hard
water laboratory may be different than other hard water environments.  I
will be interested to learn what happens when Karen reduces the lighting and
keeps all of her other variables the same. If the plant stops doing well for
her, it doesn't mean that lots of light IS needed, it just means that lots
of light MAY be needed, depending on the other tank conditions.

I have limited experience with hard water and the effects associated with
too much of certain things. Too many of the published (scientific) studies
only consider a subset of all conditions, so results are difficult to
extrapolate to all conditions. I would like to hear more about the effects
of high relative amounts of Mg, and other nutrients that are out of relative

Fortunately, most of us seem to have reasonably normal water. Some are stuck
with the extremes and stuff may have to be added (KH builders, Ca, trace
elements) or subtracted (with RO, DI) to get it closer to typical or
'optimum' conditions. In some cases, we learn to live with what we have and
try to let the plants adapt or reduce the variety, other times we can't or
don't want to.

>Subject: Hygro poly
>Of course it could be something completely different about the tank
>conditions that keeps the Hygro from growing.  I have no trouble with C
>wendtii in any of my tanks with any type of substrate.  H. polysperma will
>_only_ grow well with a soil substrate.  this is in tanks with and without
>CO2 and with and without strong light.  I don't know if this is another
>copper sensitive beast, or whether there is some other factor involved.

I have subjected H. polysperma to 0.5ppm Cu in my soft water and at that
concentration polysperma is not sensitive. THis is the concentration that
kills many algae (incl. red algae (Audinella)) and some plants like
Vallisneria. Now, polysperma and all living things are going to be sensitive
to ionic copper at some concentration. If Karen's copper levels are higher
than 0.5 (I think she mentioned 3ppm!), this is likely to be fatal. It may
be the reason that she needs soil for polysperma. The organic material of
the soil will bind with copper... and make it much less toxic. 

So in addition to excesses which create problems, we must also consider the
counter acting influences of other things (like organics or chelators). 

Are we having fun!
Neil Frank      Aquatic Gardeners Association         Raleigh, NC
      The Aquatic Gardener - journal of the AGA -  now in its seventh year!!