[clintyiu]

My 15# cylinder was about $170+/- and my pressure regulator was about $75 both prices include tax. They are both from Liquide Air. The sales person had to change the fitting on the pressure reg. to fit the CO2 cylinder.

You don't actually own any particular cylinder so don't count on it being a conversational piece in your living room. They're rusty and ugly. When your current bottle runs out you exchange it for a full one for ~$20 worth of CO2. This is part of the reason you cannot get a used cylinder. Also, like propane tanks, they have to be pressure tested and approved every ten years.

In my case 15# lasts about a year for both my reef and planted tank. This is way less expensive than leasing the bottle for $150 every year.

Becareful with custom cylinders like that from Sera. You will only get it refilled by a petshop. And you need to call ahead to have a full bottle ready for exchange. CO2 companies will refill for you if you leave it with them for a few days but they will only fill the bottle if it is CSA approved/pressure tested. Lots of hassles...

I heard that some hydroponics shops have CO2 exchange available but that was a while ago. Serious "reefers" use CO2 generators these days.

HTH
Clint