If I am not wrong, for food grade CO2, they will flush your existing tank with their CO2 before filling up. That's what the guys at Chem-Gas (the place I do top up) told me.Originally Posted by robin
I guess it isn't that important if we are using our own cylinders and for planted tanks only. Just like what we used to do for DIY CO2 which isn't 100% CO2.
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