Thanks for replies, I really appreciate it. It's always good talking to experts that have been using these things for a long time and probably come across all issues. I will indeed try inverting the bubble counter later tonight and also leave some air space.
I am very new to aquariums and CO2. Could I please just ask your advice on a couple of points?
1) Above OverStocked wrote "Your KH/PH does not effect how much co2 you need". I have seen a pH/KH chart mentioning CO2 levels. Does this chart only work if you are injecting CO2? Or can you use it if you have no CO2 injection?
2) Assuming I am injecting CO2 and 24 hours later my pH is 6.4 with a KH of 2 does this mean I am injecting 24 ppm (based on chart)? I'm just a bit unsure how the chart works.
3) My KH was 1 around 4 days ago, based on information I found on the internet, I put in 6 tsp of Bicarbonate of Soda. It appears to have increased to 2 KH now. Should I not have done this?
4) Would Bicarbonate of Soda give me a false reading in my drop checker? My drop checker is a nice lime green colour so i'm assuming everything is ok. If there isn't enough CO2 being injected would the drop checker return back to Blue?
I have 4 x 54w T5 DayLight bulbs running for 7 hours:
2 bulbs 2.00pm - 4.20pm
4 bulbs 4.20pm - 6.40pm
2 bulbs 6.40pm - 9.00pm
My CO2 also runs for 7 hours but comes on 2 hours before lights ON and shuts off 2 hours before lights OFF.
Sorry for all the questions.