Disposable or reusable CO2 cylinder?
There are 2 different cylinder types: disposable cylinders that are disposed of and recycled after emptying and reusable cylinders that can be refilled again and again. Many pet shops and gas companies can carry out the refilling. If you live in a region where refilling is a problem, the disposable cylinder can be an alternative. Should the refilling situation improve, you can always convert the disposable pressure reducer into a reusable pressure reducer in 2 minutes by unscrewing the adapter (JBL PROFLORA ADAPT U-M).
Aquarium owners who live on islands (as an example) are sometimes not allowed to transport filled reusable cylinders by ferry or plane. Disposable cylinders are then sometimes allowed!
The size of the cylinder often depends on the cabinet in which the CO2 storage cylinder is to be placed: A 500 g disposable bottle is only 31 cm high (plus pressure reducer = 37 cm), a 500 g reusable bottle with stand is already 43 cm high and a 2000 g bottle 45.5 cm high. Basically, of course, a larger cylinder is an advantage, because it simply needs to be replaced or refilled less frequently.
TÜV inspection of the CO2 cylinders: All reusable CO2 cylinders must be inspected regularly, every 10 years, by the TÜV (at least in Germany). On the cylinder you will always find - though sometimes badly legibly - the date of the last TÜV inspection and sometimes the year of the next inspection.