Carbon doser silly question

So probably a silly question but I am unsure and rather be safe and ask. Then have things go wrong by assuming and not ask at all.

So, bare with me please. Any and all help is greatly appreciated. Thank you in advance!

Carbon doser set up. Specifically the bleed down test.
It states in the instructions to connect doser to co2 bottle. Turn knob counter clockwise all the way, turn on co2, then turn off bottle, wait 15 mins. If pressure didnt move after 15mins. You are good to go.

So, I'm questioning turning the knob counter clockwise the entire way and turning the co2 bottle on in fear that the knob is going to fly off due to the pressure in the co2 bottle. Am I tripping?

Secondly, for the future as tank is not wet yet. what is a good starting pressure for the c02 and bubble count? No need for ca and alk at the moment. Never used a carbon doser before. I'm thinking 8-10# and 1 bubble every 3 sec. Trying to get about 7 in the reactor for ph as there is no demand for ca and alk in the beginning.