new to co2 question

Hi, I just set up a semi automatic co2 tank, and have a few questions:

1. I am pretty sure there is some water in my glass diffuser thing...is this
bad?

2. It seems like I can see more bubbles in the bubble counter than in the
diffuser...however, I submerged the bubble counter, and saw no gas escaping
it...is that normal...

3. when I had it set to about 1 bubble a second for the 90 gallon tank, I
didn't really notice anything coming out of the diffuser...but if I cranked
it up to 2 bubbles a second, I could certainly see bubbles. When I then
turned it down to 1 bubble a second, it looked like the co2 gas moved a few
centimeters back up the line from the diffuser towards the bubble counter
(but then stayed there).

4. So I then decided I would let the intake of a powerhead suck the top of
the diffuser, and now it looks as if the whole thing is working better,
because it is like sucking the co2 gas out of the diffuser.

5. My tank was at ph 6.4 and now dropped to 6.2 (or lower, that is the
lowest the test kit goes). I will be keeping discus and of course lots of
plants in the tank....does the co2 affect the hardness, and what buffer
should be used to keep the tank at about 6.0-6.4 ph and at acceptable levels
of hardness (5kh, dh5)...I have heard both baking soda and calcium carbonate
(what is calcium carbonate? where to buy?)

6. in that 90 gallon there are 2 bags of flourite, and 10 of those flourish
tabs...do I need anymore fertilization (would prefer not)?

okay, I know that's a lot, thanks for reading through it, and maybe
answering too

Bob