my water supplier said ph rises when left sitting
I think that is incorrect. You would have to let an aweful big container just sit around for days on end to get it to jump that high. Besides its not just sitting in your tank. There is current, filtration, airation etc.
This is taken from a previous post by
fishsmurf and covers PH VERY well.
Before explaining KH + GH it is probably best to understand that there is a third property that makes up the water chemistry triangle in a freshwater tank, this third property is PH. All three of these properties have an effect on our water chemistry.
PH is used to denote whether the water is acidic (PH reading below 7), neutral (PH reading of 7) or alkaline (PH reading of above 7). PH is fundamental in providing a good environment for our fish to live, all species have a PH range that they will be happiest in, therefore the more constant & stable we can keep the PH the happier our fish will be. For the beginner is is probably easier to match our chosen species to the PH we have as opposed to trying to adjust PH to suit a specific species.
KH refers to the ability of our water to resist change in PH. This ability to resist change is known as carbonate hardness or more commonly buffering. Therefore when a KH reading is taken, the higher the KH reading the stronger the ability to resist changes / fluctuations in PH. A strong buffering capacity is beneficial if you have the PH that you require to keep the species of fish you are interested, however if your are trying to alter your PH for any reason a high KH reading is going to make it more difficult to effect this change.
Finally GH or General Hardiness, when water is referred to as hard or soft GH is the property being referred to. Water hardness is measured on two scales either DH (degree's hardness) or the chemical compound measured (CaCO3) in ppm (parts per million), both of these measurements can be used although most test kits will utilise the ppm measurement system. The two systems equate as:
0 - 4 dH or 0 - 70 ppm = very soft water
4 - 8 dH or 70 - 140 ppm = soft water
8 - 12 dH or 140 - 210 ppm = medium hard water
12 - 18 dH or 210 - 320 ppm = fairly hard water
18 - 30 dH or 320 - 530 ppm = hard water
As mentioned at the beginning all three of these properties are distinct, however it is important to realise that PH, KH & GH all interact, therefore any alteration to one will have an impact on the other two. Having said that with careful monitoring and control it is possible to make adjustments to these properties without having to rely on shop brought chemical additives such as PH Down.
Two thing really that should stand out would be:
1) A stable pH is more important than aiming for a specific pH.
&
2) It's better not to aim to alter the water for the specific species you keep but rather to adjust the species you keep to match the water condtions you have.
before i had fish water was just for washing in didn't realise how complicating it can be :stupid:..... sorry billy this is your thread 
