With the fish you are keeping you have no reason to worry about either the KH (alkalinity) or GH (Total hardness) of your water unless you are experiencing problems which could be connected with them. I would recomend doing a pH test once every two weeks though to check on its stability, a falling pH may indicate more water changes are needed.
Alkalinity (or KH as it is incorrectly known in fish keeping circles) measures the ammount of calcium bicarbonate in the water which is the waters natural buffering system. This buffering system prevents organic acids released from the nitrogen cycle from causing the pH to drop, weekly water changes top up the ammount of calcium buffers so the ones used up are replaced. A KH above 4 is required for a stable well balanced aquarium.
GH (or Total Hardness) is the is the measure of calcium and magnesium present in the water combined and is unaffected by organic acids or boiling, this is the term reffered to when speaking of hard or soft water. Below 10 degrees GH is soft and above is hard, tropical fish generally preffer a hardness between 5 and 12.
pH measures how acidic water is by measuring the hydrogen and hydroxide levels present in the water, 0-6 is acidic and has a higher level of Hydrogen present, 8-12 is alkaline and has a higher level of Hydroxide present, if there are equal levels of both the pH is 7 and this is called neutral. Most tropical fish preffer a pH of between 6 and 7.5.
