A CO2 bottle on a marine tank might be either on a PH controller, where CO2 is percolated through the water to lower PH, or on a calcium reactor, where the acidic CO2 dissolves the calcium into solution.
Ozone is just piped through the skimmer, the skimmer is an ideal reactor chamber for it. You could just use an airstone, but the skimmer is too perfect for the job already.
The ozone gas is a super powerful oxidiser, and so it increases the oxidation reduction potential of the water, and sterilises it too. You measure the ORP in millivolts with an ORP probe, and a reading of between 300 and 350 is a good range, although some run as high as 395. Any higher is dangerous.
There's no consumables with ozone, except for the silica gel air dryer (as the input air needs to be very dry), and when that's full, you can either microwave it or replace it.