What is there to do. Taking you are using a Pub type or BOC type bottle which on a tank of that size you will end up with.
1) Screw regulator onto gas bottle. Tighten the nut with a spanner. There will be a sealing washer supplied that goes between the mating faces .
2) Screw the needle valve onto the Regulator. You can buy ones with this and the solenoid valve already assembled. This would be the best one for you in this case.
3)Attach a length of Co2 hose from the needle valve to the bubble counter. The bubble counter will need filling with water first or you wont see any bubbles
4) Attach a length of Co2 hose from the bubble counter to the chosen diffuser of your choice. This will depend on you set up which one you choose. I use a Ceramic airstone on the inlet of a pump in my sump. This works for me.
5) Plug in the solenoid valve to the mains socket and Turn on. Close the Needle valve and turn on the bottle. If its a Pub type bottle then it will have a rotary valve on the top.
6)Open the needle valve slowly watching the bubble indicator and stop when you reach the desired BPS.
7) Get some soapy water and spay it on all the joints to check for leaks. They will be very evident using soapy water.
8 ) Unplug the solenoid valve and plug it back in through a Timer so you can set it to come on and off when you need it, my one comes on 5 hrs before lights on and off 3 hours before lights off. Works for me with my present stock , lighting level and food availability.
Its simple. There is nothing to go wrong . Just use decent kit. My Reg complete with solenoid and needle valve was about 50 quid and works perfectly.
A tip is weigh the bottle with the Reg fitted . Weigh it again in 7 days time and you will see how much gas you have used. Gas is supplied by weight.If you had a 5 KG bottle and used 1kg in a week then you have 4 weeks left left approximately .
simon