So I felt like I was being ripped off paying R59 to replace a 300 gram Sodastream bottle to fit on my Sera CO2 regulator and decided to make the Sera regulator fit on an Afrox bottle which costs R132 for 6 kg and lasts much, much longer.... Check the pic below - it turned out to be a relatively simple mod and the most difficult part was getting the valve off the Sodastream bottle... I discarded the empty bottle after this, because it was manufactured in 1999 and still in circulation, just nicely covered in a blue plastic jacket so you couldn't see what the actual bottle looked like ! In the picture: 1. CO2 bullnose fitting from Afrox - R165 (a bit of a rip if you ask me, but still worth it) 2. 3/8" to 1/4" male-female socket - R10 from HoseFit 3. Valve off Sodastream bottle - R59 if I count what the refill cost 4. Sera CO2 regulator bought in kit some time ago I needed to use the valve from the Sodastream bottle, because the Sera regulator has a cap screw that opens the valve and that is where you regulate the pressure. The Afrox bottle is Suremix 100 - the stuff they put into cola and beer at the dispensing machine or bar counter - it's food grade CO2 and apart from the once-off R140 refundable deposit, it costs R132 a pop to exchange the bottle for a full one. PS. I don't work for Afrox... it's just the most hassle-free way of getting a full bottle of CO2 to me.