Re: substrate Qs

Andrew wrote in response to my response:

> > 1/2 inch of worm castings and peat is TOO MUCH organic material and
> > too fertile. This would almost certainly lead to persistent green water
> > problems. I would suggest 5% by weight of either worm castings or
> > peat mixed with 60% ordinary sand and 35% of the Terra Stone clay.
> > Also I would use a 1" layer of sand on top of that as a seal and
> > either pebbles or a little gravel to help hold the plant stems in place
> > during the initial planting.
> > 
> 	Thanks, Steve, for your response.  A couple more questions come
> to mind: Are you suggesting mixing the organic material, the sand and the
> clay together in one layer?  I initially thought I would separate the
> orgaic material from the clay/laterite layer with a layer of sand/fine
> gravel.  Does it matter? 

my feeling is that the organic material needs to be mixed in with
the mineral and inert materials. they work together to facilitate
uptake of nutrients. you could also have a stratified substrate where
you had clay & sand in the bottom layer and then a clay-sand-organic
mix in the middle layer. I mentioned fritted trace elements but I suspect
that may be hard for some people to find so in lieu of that, you could
mix ordinary soil with the clay  too. The only critical ratio that I
know is the ratio of organic material should be about 5% of the total.
The clay is an excellent source of Fe; better than granular laterite because it
has a surface area more than 1000 times greater than the granular laterites.

> >  The Ca and K in the substrate are of
> > little use to the plants. These nutrients must be in the water and
> > should be supplemented regularly along with Mg at water changes or 
> > in a daily regimen like PMDD or Dupla drops.
> > 
> 	Hmmm.  Why would nutrients like Ca and K in the substrate be of
> little use to the plants? I would think that heavily rooted plants like
> Crypts and Swords would be able to use these nutrients in the substrate
> just as well as they would be able to use N, Fe Mg etc.  Is there
> something about Ca and K (and presumably other nutrients) that makes them 
> unavailable via root uptake?  What am i missing in the nutrient uptake
> and transport theory here?

According to all three of the scientific experts I consulted with, they
said Ca, K & Mg must be in the water. Everything else (except CO2)
can come from the substrate. Some plants even  get CO2 through their
roots. Perhaps Paul K or Dave Huebert will offer some explanation
for preference of that mode of uptake.

> 	BTW, thanks also for your posted tips regarding Ca defieciencies
> in Swords:  my Swords have improved colour since I began adding small
> amounts of Dolomite powder occasionally.  My Jade Sword is beginning to
> regain its former dark (jade) green colouration.  I haven't seen any
> negative results of adding the powder directly to the water column, though
> it does of course take a long time to dissolve.

Paul Krombholz recently reported that dolomite lime powder dissolves very
slowly. Calcium phosphate formations on the surface of large crystals can
effectively prevent limestones from dissolving effectively. I recommend
powdered calcium carbonate from your drugstore. It's fine enough powder
that it will stay in suspension long enough to dissolve (I think but
have not proven scientifically).
> PS  Does the company which ships the terra cotta clay not have available a
> chemical breakdown of the clay?

I have not contacted them to find out. If someone would do so and get back
to us that would be great. My suspicion is that the clay does not contain
many impurities which we would consider beneficial micro-nutrients. That's
why I think trace nutrients should be added either as FTE or from ordinary
soil (top-soil or subsoil) which will contain a wider range of micro-nutrients.
I suspect that this pottery clay is almost entirely iron and aluminum
silicates and iron and aluminum oxides. But it could contain other elements
too. I just don't know.

 Steve Pushak - spush at hcsd_hac.com - Vancouver, BC, Canada

There are no signposts in the sky to show a man has passed that way
before. There are no channels marked. The flier breaks each second
into new uncharted seas. - Anne Morrow Lindbergh