My tanks chem values - any thoughts?

I leave my CO2 running at night. I have checked pH before my lights come on and I see no difference--or at most a .2 difference.
My fish are all fine and so are my plants.

KH measures the carbonate/bicarbonate buffer in the water. In normal tank rages of pH, CO2 addition does not change the KH.

Whether or not to shut off CO2 at night (many folks do not bother, many other do - either paired with the lights or starting and ending an hour before the lights) is likely to be a function of your CO2 levels. If you are running >30ppm toward the end of the light cycle, you might OD during the dark cycle. Try it for a few days, check just before lights-off and just before lights-on to get the maximum range in your tank.

HTH

As RTR says, kH is not affected by CO2. It is your buffering parameter(stabilizing the water) and if it's 6 it is perfectly safe to inject CO2.
I would double check your kH and gH out of the tap after a few hours of sitting on the counter, and make sure your initial readings are accurate. It's a very large drop from 8.2 to 6.8
and perfectly possible, but just seems quite a drop to me, so I'd double check at least the kH.
If you have an established tank and it's well planted, the need for an ammonia tester is minimal. Even in a new tank with lots of plants and a few fish there is little need to test for ammonia.
You are reporting(6.8pH/6kH) a CO2 ppm of 29. This is very high and you want to make sure your tank doesn't go too much above that at night. I would bring it down to 22 to 25 during the day and check it in the morning just before or after lights on to see what it's like at that time. This will give you a reference as to how high you can go during the day and still be assured of a comfortable environment for the fish.
My tank's regularly violate the kH/pH rule, sometimes going into the mid 30's with no problems for the fish, but I wouldn't recommend pushing the CO2 to others. I also have a bunch of wood in my tanks and this always plays with my pH reading.

What is the size of your tank and what is the lighting situation?


Len

Tannins, tannic acid, in the water always pushes the pH down farther than the GH would indicate, giving an artificially high CO2 reading. It is possible to differentiate, but it is not easy or really worth the hassle.

The tables for pH/KH/CO2 make the assumption that carbonic acid (from the CO2) is the only acid present. With peat, plenty of wood, heavy mulm, there will be acids other than carbonic which will be read from the chart as CO2, making the CO2 reading exaggerated.

There is nothing wrong with your KH, other than the instability of the readings. Check first with your utility to see what you should expect for carbonate hardness, and if they use multiple water sources - they may use water with varying KH depending on need. My utility has one reserve well, much harder than the rest (different aquifer) which is used only in high demand periods - when in use it does increase the KH reading I see.