Re: CP digest 445

Wayne Forrester (forrestr@mendel.Berkeley.EDU)
Thu, 24 Aug 1995 09:27:05 -0700 (PDT)

On Wed, 23 Aug 1995, Ellen York wrote:
Can anyone tell me or
> suggest asource for information on the types and mechanisms of this
> process, the specific needs which are satisfied in Nepenthes and other
> CP genera (or if tolerances are known) species, by the available types
> of RO and the products of each.
I don't know if anyone has looked at specific tolerances of
particular CP to dissolved materials in water. Much of the info is
anecdotal; many plants are sensitive to dissolved metals and salts and
RO gets rid of most of this. If anyone out there knows of studies
investigating tolerance of various CP (or orchids) for salts/metals I
would also be interested in hearing about them. There are many RO units
advertised in the back of the American Orchid Society Bulletin, which
you may be able to find at a local library.

I assume that not all RO is created equal. Do any
> systems leave any minerals in the water?
They all leave some dissolved minerals. No system is perfect. I
suspect that all systems are created more or less equal, in the sense
that they all remove the lion's share of dissolved materials. Probably
any well designed system will reduce levels sufficiently. I think the
main considerations are cost of the unit and capacity. The systems I've
seen advertised often have 10 - 30 gallon/day capacity. There are many
larger systems available, but they cost more.

Is RO as corrosive to metal
> plumbing as distilled?
Generally, as salts are removed from water it is less corrosive.
I have always thought that distilled water was less corrosive. You may
want to use plastic plumbing to protect the water from picking up metals
from the pipes anyway.

How does pH change with RO?
I suspect, very little. RO basically forces water through
membranes that are relatively impermeant to various ions. I doubt these
membranes would have any affect on H+ ions, and I doubt that removal of
the salts/metals present in water will affect the dissociation of water
into H+ and OH-.

How does it affect
> the efficacy of pesticides?
Can't answer this one.

Hope this is helpful.
Wayne Forrester
> Your consideration of this subject will be greatly appreciated!
> Ellen York, Greenhouse Manager
> University of Pittsburgh, Dept of Biology
> Pittsburgh, PA 15260