Re:Re: Electro-Right, RO-Right, etc.

     >> The bottle of Electro-Right states "Deionized water is too pure for
     >> freshwater tropical fish" and "these "hydrominerals" are necessary for
     >> proper gill function, regulation of blood pH, oxygen uptake, and other
     >> metabolic processes".
     >Frankly, this stinks of fraud.  Deionized water is NOT too pure for
     >fish to live in in any way.  There is no essential mineral fish need
     >that is not more easily obtained from their FOOD--their ability to get
     >some minerals out of their water is at best a sort of back-up in the
     >event their diet becomes partially deficient in an essential mineral.
     >(And even then it's not always enough to save the fish from developing
     >symptoms of the deficiency.)  As far as your fish NEEDING the minerals,
     >that's certainly true, but any statement to the affect that fish need
     >trace minerals in their water is, to put it politely, suspect.
     Sorry Nathan, but you seem to be confusing the nutritional requirements for 
     minerals with the osmotic requirements.  Freshwater organisms maintain an 
     internal osmotic concentration of salts much higher than their surrounding 
     environment.  Gill membranes are extremely permeable to water and provide 
     the greatest inflow of water, so excess water excretion and salt retention 
     becomes the problem.  Salt are lost mainly through urine and feces.  Some 
     salts are regained with food, as Nathan pointed out, but the main intake is 
     by active transport in the gills from the surrounding water.  This process 
     is metabolically expensive--it requires a great deal of energy.  Deionized 
     water IS too pure for freshwater tropical fish, as they would expend a lot 
     of energy and eventually lose the salts in their tissues and die.  Also, I 
     an unaware of any fish that REQUIRES soft water to live, and could only do 
     so for any long periods of time if the Na and K levels are fairly high.
     Marine organisms have just the opposite problem--their internal salt 
     concentration is lower than their surrounding environment, so their problem 
     becomes one of retaining water while excreting excess salts.  Marine fish 
     drink water constantly and have a highly concentrated urine, while 
     freshwater fish never drink water and have an extremely dilute urine.  
     Amazing, eh?
     A good general reference on this topic is Animal Physiology, by Knut 
     Schmidt-Nielsen.  I have a masters in environmental physiology, and I used 
     to do a lot of work on the osmoregulation of aquatic organisms, in a former 
     life.  Fascinating, but the pay sucks.
     BTW, who in their right mind would fill their aquarium with de-ionized 
     water anyway?