Originally Posted by Olympia
My pet smart sells true twig catfish... I never thought they were rare. Also cheaper than my LFS's whiptails.
If I remember correctly, isn't 0.1 of a pH a ten times difference? So 7 and 7.3 are a 30 times difference? I'm not totally sure how pH affects fish though (probably in that article Byron wrote that I didn't get a chance to read yet!)
Hardness can be a problem, a fish kept in too hard water gets kidney problems, since it's kidneys are put through much more strain filtering minerals than they are adapted to. This of course shortens lifespan.
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Each degree, being from say 6 to 7 or 7 to 8, is a ten-fold increase/decrease in acidity depending which way you're going. So if the pH is 6, the pH of 7 is 10 times less acidic. And being a logarithmic scale, the change from pH 7 to pH 8 is 10 times 10 or 100 times less acidic that pH 6. You can see how crucial this is to the fish, if he is meant to live in water that is 5-6 (which Farlowella are) and we place him in pH 7.5 this is major.
Normally a few decimal points will make little if any difference, though there are situations where it might. One is when going either side of neutral, that is significant.
The pH of the fish's blood is impacted by the pH of the water entering the cells, as it does continually. The fish has to work to maintain a constant pH in its blood, this is part of the physiological homeostasis, and the further the pH in the water is from the pH that nature intended for the species, or to which it has evolved over eons, the more energy it takes and it causes stress. The stress article will hopefully help here.