Zambize, yes they are helpful in understanding fluctuating pH. kH is a measure of the carbonate hardness of your water (i.e. the concentration of carbonates and bicarbonates). It is also an indicator of you water's buffering capacity. Buffering capacity refers to your water's ability to have acid added to it and neutralize this acid without significantly changing the pH. Therefore, if you have low kH, your water does a really bad job of maintaining the pH. This is why it is important. I just wrote an article on pH in the article section of this website. You can look at that article as well.
gH is general hardness. It is less important for pH concerns, but is still a useful measurement because it tells you how hard your water is (hard water tends to lead to high pH and vice versa - however, these are just guidelines).
pH, gH and kH are intimately tied. You cannot just focus on one and ignore the others, especially in your case where we have tried multiple things.
Zambize - spongebob is right. This is one reason that only using products such as pH up and pH down do not work for long. If you do not attack both the buffering capacity of your water and your pH then you will not maintain whatever value you get your pH to for very long. This is why it is useful to do things such as add limestone or crushed coral to raise the pH - it attacks both fronts.
I still say get a kH reading for your own peace of mind (so you know what is causing the huge swings in pH) and then either filter over peat moss or buy water.
Right now I'm attending to fish mysteriously going belly up today, but I can't wait to read the article. I will get the tests as recommended, and I'm assuming you recommend drop tests. I just quickly used some really inaccurate and hard to read strip tests and got a gh of 180ppm, top of the chart, and a kh of at least 120ppm, not far from the highest.
