05-11-2011, 07:46 PM
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This is going in the wrong direction, and the fish will be the losers.
First, where did you read that Tetra prefer a pH of 7? Nothing could be further from reality. No fish needs a neutral pH, it is completely un-natural since all natural waters are either acidic or basic/alkaline according to the substances they flow over/through/in etc. And tetra from South America mainly live in very soft and acidic to slightly acidic water. A very few species live in very soft and slightly basic water. But whichever, the hardness factor is equally important.
I would absolutely not use calcareous sand or gravel for the substrate. This will raise the hardness (and corresponding pH) far too high when it is not necessary.
It is always safer (and less expensive) to use what comes out of the tap if this is at all possible. Some minor adjustment can be made, with natural means, depending upon the fish species. As you are in the Pacific NW your tap water is probably soft. The pH may vary according to the source and what if anything the water supply folks put in it. If you could give me your tap water hardness and pH I can offer further advice as to what if anything is necessary.