Originally Posted by dazeek
Thanks Byron. I'll have to wait til monday to get the info from my water company unless i can find a test kit at the aquarium store over the weekend.
We dont have any rocks in the tank other than fake rock looking decorations that were bought at the aquarium store. The gravel we have is just regular pet store aquarium gravel. I dont know the brand but I do know that it was for freshwater aquariums.....i'm not thinking that helps you? We also do not have any driftwood in the tank (in case that would change things at all)
On the gravel, some contains calcareous rock and is suited for marine tanks (e.g., crush coral) or rift lake cichlids or perhaps livebearers. If it was in a bag, it should say somewhere. If it is "regular" quartz gravel, it will be inert (no effect on water chemistry).
With that out of the way, the pH should not climb higher than the source water. However, one small point here, when you tested the tap water pH, did you let the water sit for 24 hours? This allows the CO2 to dissipate from the water and the reading will likely be higher, depending upon the amount of dissolved CO2 in the water. My tap water goes up maybe .1 or .2 at most, but in some places it can be much more. If you didn't do so before, run a glass of water and let it sit overnight, then test the pH and see what it is. The tank should remain at or below whatever that pH is, assuming there is nothing calcareous in the aquarium.
Over time the pH will tend to lower, as the water acidifies. Knowing the hardness of the source water will tell us what to expect; the softer the water the quicker and more it will acidify through natural biological processes. We can discuss this after you have the hardness numbers. I wouldn't wast money for a hardness kit, you really only need it once for the source water, unless you intend to be adjusting the tank for a specific reason.
Real wood will tend to assist in the acidifying, as would peat. But again, this will be countered by the buffering determined by the KH/GH.