I made Open Cola once, and hooked it up to CO2 canisters and a beer tap (the other tap had home made beer). It's certainly better than mixing with soda water or using a SodaStream.
The trick to have well carbonated beverages if all you have available is a sodastream-like device:
- cook the water to remove any other disolved gasses
- Cool it down to as cold as you can. A sludge of ice and water is very close to zero °C
- keep some ice unmelted
- carbonate
This is a bit annoying to do especially step one (I skip it, it seems to help bit not to a huge degree) but it helps making very carbonated water to mix with the sirup
The trick to have well carbonated beverages if all you have available is a sodastream-like device:
- cook the water to remove any other disolved gasses
- Cool it down to as cold as you can. A sludge of ice and water is very close to zero °C
- keep some ice unmelted
- carbonate
This is a bit annoying to do especially step one (I skip it, it seems to help bit not to a huge degree) but it helps making very carbonated water to mix with the sirup