It really depends on the size of your aquarium. For example, for a large (i.e. 90g) tank, a 9 oz CO2 tank would run out within a few days. For a smaller, 2.5g nano tank, for example, it may be OK.
Keep in mind that the prices of CO2 tanks do not rise linearly with their sizes. For example, I would pay the equivalent of 70 USD for a 5 lb tank, but a 10 lb tank costs 80 USD. A 20 lb tank costs 120 USD.
Also, refill costs are the same (for me) regardless of tank size.
As for other equipment that will be required, you will need a regulator and a needle valve, at the bare minimum. Another high priority piece of equipment is a check valve, to prevent a possible back siphon of water from destroying your regulator. Other optional equipment include a bubble counter, a solenoid, a diffuser and a drop checker (with a 4 dkH reference solution).
If you decide to get a standard CO2 regulator with the CGA320 fitting, you will also need a CGA320 to a paintball canister adapter. This will also allow you to switch to a regulator CO2 tank if you wish to upgrade the size in the future.
Keep in mind that the prices of CO2 tanks do not rise linearly with their sizes. For example, I would pay the equivalent of 70 USD for a 5 lb tank, but a 10 lb tank costs 80 USD. A 20 lb tank costs 120 USD.
Also, refill costs are the same (for me) regardless of tank size.
As for other equipment that will be required, you will need a regulator and a needle valve, at the bare minimum. Another high priority piece of equipment is a check valve, to prevent a possible back siphon of water from destroying your regulator. Other optional equipment include a bubble counter, a solenoid, a diffuser and a drop checker (with a 4 dkH reference solution).
If you decide to get a standard CO2 regulator with the CGA320 fitting, you will also need a CGA320 to a paintball canister adapter. This will also allow you to switch to a regulator CO2 tank if you wish to upgrade the size in the future.
