Originally Posted by crs1945
The pH is from the tap But after letting it sit for 48hrs. it now reads the same as the tank water. This is what some of the books said to do, allow the tap water to sit for 48hrs. before doing a water change and I can see why.By the way we have well water.According to the test kit info. the kH is at the lower end of normal and the gH is slightly above norm by 1 degree.
Perhaps I can explain this. Tap water usually contains some CO2 (carbon dioxide). CO2 causes carbonic acid which lowers pH. So when you measure the tap water pH right out of the tap, if there is a lot of CO2 in the water it will be lower than the actual pH. Letting tap water sit overnight before testing allows the CO2 to dissipate out, as it naturally will; or you can shake the water briskly. The pH will then be "true" as it will be the actual pH of the water.
When it comes to water changes, there is no need to let water sit out. However, if the variation between tank and tap is significant in pH and hardness, a smaller volume of water might be preferable to doing a massive water change.
The pH is linked to hardness, but can be high even with low hardness depending upon everything that is in the water. At this point, we should review everything, because I am a bit confused by the numbers being tossed about in this thread.
First, what is the hardness (GH and KH) and pH of your source water out of the tap [using the pH after the water sits]?
Second, what is the pH of the tank water? Presumably hardness will be the same, unless you have calcareous substances in the tank to raise it.
Third, what fish species do you want to keep?
There are easy ways to lower hardness and pH [the two must occur together in most cases, though not always] if that is necessary. The above answers will tell us this.