Hi Dean
What size is your tank do you have the pH, gH and kH readings a 6kg bottle last me about 6months on a 180ltrs @ about 2/3 BPS
BOC cannot not fill them i'm afraid BOC will not fill any bottles but there own you also you have to have an account with them and you need to a minimum demand of 25kg a month
If you using a paint ball bottle the only place to get these filled would be local paint ball center or gun smith
Also a downside is your need to find some way to prevent the paintball bottle falling over the bottle must remain upright to prevent liquid CO2 flowing down the line
F.E and Co2 bottle have flat bottom unless you can get a paint ball bottle with flat bottom you may have a problem here you can buy bottle stands but that an extra cost. Also the regulator will sit on top of the bottle and not to the side like on F .E or CO2 bottle
Id only consider using a Bottle that small on a Nano tank up to 100 ltrs tank for anything over 100 ltrs i would use a 500g/2kg bottle
If you can afford An F.E or co2 bottle you be better in the long run easy to get filled last longer and will stand upright on its own also regulator will be on the side
I got my first 2kg CO2 bottle from ebay for £25 about 5 years ago and it was filled must remember tho buying your own CO2 bottle it must be inspected and pressures tested every 5 years and certificated before some fillers will fill you own bottle
http://en.wikipedia.org/wiki/Gas_cylind ... er_testing
May be different with F.E and Paint ball bottle that's why
I use a pub gas supplier he delivered me two of his 6kg bottle a while ago when one runs out swap them over give him a call he changes it next day for me i don't have to worry about paying for bottle testing & certification anymore.