On 27 Mar 2006 02:18:23 -0800, "Frank"
wrote:

ML wrote,
it appears that I need to change it every once in a while.......

I don't like using crushed coral or crushed oyster shells to raise pH
to a target value less than pH 8.0. In an established tank of fish used
to a pH 6.5, it would raise the pH way to fast, passing your target of
pH 7.0, or whatever. I found that a marble chip or two raises pH much
slower. By slowly adding baking soda over a few days, you can raise
your pH to the target value you want, and then hold it there with a
marble chip, or two placed in your filter's box....

new fish that died.....
established fish that died.....

Most people kill their new fish by osmotic pressure shock (used to be
called pH shock), and I can see how that happens, but that's not what
killed the established fish! An aged tank, low pH (lowered TDS), then a
large water change using water with a high pH (raised TDS) would/could
cause osmotic pressure shock, but you said your tap water has a low pH
(lowered TDS). Not enough difference in TDS to make enough of an
osmotic pressure change to kill fish! ....
Nope, I would stick a marble chip in the filter and look for another
reason as to what killed the fish, being that *both* the new fish *and*
the old fish died. Just adding my 2 cents worth............. Frank

And 2 cents from Frank is worth a few bucks next to many of us.

-- Mister Gardener