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Re: ro vs deionized water


In a message dated 4/10/01 11:31:38 AM, MesoGED at aol_com writes:

<< enlighten me on the difference between ro 
and di water/ my reason for this question is that for many years now i have 
been using water softener pillows from aquarium pharmaceuticals to soften my 
water. >>

Your question needs to be rephrased. Your water softening pillow is not a 
deionizing, mixed bed, ion exchange unit but a cation exchange unit that adds 
sodium ions in place of calcium (or other divalent) ions. Aquarium 
Pharmaceutical also makes a tapwater purifier which is a true deionizer 
(mixed bed resins). The question therefore is what is the difference between 
softened water and deionized water and R.O. water. Here is the brief summary 
of what each will do.

Water softener exchanges sodium ions for calcium and magnesium and does not 
reduce the conductivity. This water is satisfactory for many fish, not all. 
Typical conductivity reading could easily be 600 microsiemens or more.

Deionizer removes most of the ions, cations and anions and the water will be 
low in conductivity and unsuitable by itself for aquarium use, but useful 
when blended with some tapwater to get intermediate total dissolved solids or 
conductivity. Typical conductivity reading could be 20 microsiemens or less.

Reverse Osmosis water is close to distilled water or deionized water but may 
still contain some conductive ions. It is also useful for blending to get 
intermediate values.
Typical conductivity reading could be 20 microsiemens or more.

    The common misconception about the water softening pillows can be carried 
over to a concern about the health of people drinking that sort of water. 
Sodium ions are essential to the human body, but an excess is harmful, 
especially for people with high blood pressure. To some extent the same is 
true of killifish. Many of them really like salt water, others don't. 
Brackish water killies like salt, South American annuals do not.
    The other question about how it can be soft and still conductive was 
answered here a few days ago. They are different but sometimes related 
factors.

Lee Harper
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