Re: Reconstituting aquarium water

> From: "David W. Webb" <dwebb at ti_com>
> Date: Wed, 11 Dec 1996 12:26:08 -0600
> Subject: Reconstituting aquarium water
> I've been thinking about the reconstitution problem from an automatic water
> changer perspective.
> Since I'd be using RO water, there could be a problem with overly soft
> water.
> What I'm thinking is to put an in-line cartridge between the RO unit and
> the tank and fill it with limestone and dolomite chips.  Some of the
> limestone and dolomite would dissolve into the RO water as it passed
> through and enter the tank system, later to exit the tank via the overflow.
> This would not have the same effect as putting limestone or dolomite
> directly in the tank, because the tank water would not continuously
> circulate over the carbonate rocks.
> However, this is another, simpler alternative.  Since I'm already doing a
> continuous water change, placing a small amount of limestone and dolomite
> directly in the tank might have the same effect and keep the water from
> becoming too weak.

I don't use RO water but my tap water is extremely soft, so I have to
add something to buffer the water if I want to avoid pH crashes. I used
to add a combination of baking soda, calcium carbonate tablets, and
epsom salts whenever I did a water change, carefully measuring water
hardness and alkalinity each time. I got tired of that, and tried just
sprinkling a small amount of dolomite gravel around the tank.  This 
works very nicely, and requires no maintenance on my part.  The pH of
the tank seems to reach a point of equilibrium; if acids start to lower
the pH, the calcium carbonate dissolves more quickly.  After some trial
and error you can find how much dolomite will keep the pH just where you
want it.  The equilibrium point seems to change with temperature: in the
winter my setup stays at 75F, but it may hit 80F in the summer.  The
equilibrium pH seems to get higher as the temperature goes up, even by
a couple of degrees.  Skipping water changes may increase the pH also.
Still, I haven't had a pH crash since using this technique. My pH stays
between 6.6 and 7.4, just where I want it.

Glen Osterhout