Bob A wrote:

One other question, since I'm now using RO/DI water, and RO Right, the RO
Right does not register on my GH test. The (TINY) instructions on the
packaging say that typically GH tests measure Ca and apparently there isn't
much in RO Right.

How important is Ca in an aquarium, both to the fish and to the plants?

For a complete label printout, go to:

http://www.kentmarine.com/ror.html

Key quote:

"General hardness or GH tests usually only measure calcium & magnesium content
and are a poor substitute. Do not greatly exceed the recommended teaspoons even
if your test indicates different!"

I use pure reconstituted RO water in my tank (no tap water). I use one teaspoon
per 10 gallons of change water for a 30% weekly change. My plants show no signs
of calcium deficiency. Snail and shrimp shells do fine too.

Do you have actual indications of a calcium deficiency, or is this a general
concern?