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Re: Reverse Osmosis Units

You wrote: 
>This is all pretty theoretical right now, but if I were to get an R/O unit
>to treat our Ph 7.8/hard Central Florida water, what should I look
>for in such a unit?  I have no idea what any of the abbreviations in the
>ads mean, and I'm not too sure exactly what makes one kind better than

It's hard to beat Fredrik's response. I bought mine at Price Club quite a few 
years ago, and the original membrane is *still* going strong.

The following is some added info, lifted from this month's Northern California 
Killifish Club News (copyright '97) As author and editor, I can authorize 
reprint here. All other rights reserved. :-)

                               What’s RO?

Reverse Osmosis, "RO," is a process where small molecules (CO2, H2O, etc.) can 
be forced through a permeable membrane by pressurizing the "salty" side high 
enough to overcome the normal forward pressure of osmosis.

Units to do this cost from $100 to $300 at Home Depot or Price/Costco. I saw 
one in a thrift shop, Sunday, for $5, and that had another 30% off! Didn't need 
it, so didn't buy it. [Went back and got it the next week.]

Osmosis is the tendency for a pressure to develop across a membrane as the 
purer water tries to dilute the saltier (or hard) water and raises its (the 
salty side) pressure when water moves through the membrane. Just raising the 
pressure on the saltier side further (e.g., by tap pressure), will reverse the 
flow and slowly give surprisingly pure water as the output. Mine comes out 
around 30 ppm of tds, from my input water of over 450 ppm of tds (parts per 
million of total dissolved solids). Triple-distilled water is, practically by 
definition, 0 ppm of tds.

A carbon filter and a sediment filter are mandatory to protect the membrane and 
keep chlorine (another small molecule) out of the output water. Overflow from 
the hard-water side can be run into your drip-irrigation system, for most 
plants tolerate hard water pretty well (not all, so protect your Begonias and 
Azaleas or whatever -- I'm no botanist).

I assume fish somehow adjust their own “permeable membrane" to balance the 
salty fluids in their body to the outside water. A little salt in the water 
means they are fighting considerably less osmotic pressure. You can also 
visualize why sudden changes in hardness and/or salinity can be most stressful 
as they fight to make the complex changes required in their gills and skin to 
balance bodily fluids, again.

End RO Note.....


- -- 

Wright Huntley (408) 248-5905 Santa Clara, CA USA huntley@ix.netcom.com