Hey all so I recently setup a 55 gallon planted tank and wanted to setup co2. I searched for weeks and could not find a place to get a 5lb or larger tank that was open on weekends or even after 4:30 during the week so the only option right now is a 20 oz tank. Does anyone run a 20 oz on a 55? how long would that last?

I have never run such a small CO2 cylinder before, but I would say 2-3 weeks, at best.

Slightly off topic, but does any know where you could get large co2 tanks besides welding gas supplies or home brewery shops? that's the only places I looked for and if there are other places that offer co2 it would help out

fire extinguisher places might have. In Winnipeg that's where I go to get my tank filled and I also bought my tank from them

Hydroponic garden supply stores will often carry CO2 tanks as well

You can get them on Ebay or Amazon. about $50-$60.

If you go this route, be sure to ask about the hydro testing date on the cylinder. You don't want to purchase a cylinder only to find out that it requires recertification the following year.

https://beveragelements.com/beverage...iABEgLwPfD_BwE

Also, for reference, my 30 gallon tank takes about 2 months to go through a 24oz paintball tank running for about 9 hours per day. I think 3-4 weeks is a pretty fair guess.

My 29g uses 24oz tanks and I get almost 2 months out of them. Debating a 55 gallon and assuming I might need to go full size.

Hard to predict how long CO2 will last in each tank as it is combo of lots of variables. Not only how much we are adding but how much we are losing! I have had a 20 gallon long and 75 gallon side by side and using the same amount of gas in both!
My first thought for CO2 tanks, is to go used as they are far better value in my area and my methods of use. That leaves me looking to the local Craigslist or local shopping type methods. Restaurant closeout dealers may also have tanks as they are used for soda and beer. Local music scene? Lots of bands use CO2 for the "fog" and bands break up all the time, selling off the tanks.
I would put lots of effort into finding a larger tank before going through the constant hassle of breaking down to refill and replace small cartridges. There is a lot of potential for damage as well as lost gas through leaks and the less often it is done, the better.
Regs and attached parts may be lost due to damage more often than due to wearing out! Even the best of us may cross-thread things at times?

If I'm not mistaken, the tanks you get on Amazon/ebay ship empty. Just in case this prevents any misunderstandings here..