Co2
I have a cylinder that can be used for CO2. It is marked for nitrogen, but I took it to a gas place and they said it would need a C02 valve and then hydrotested again. I also have a nice DIY bubble counter I could send with the tank for free. I have a glass diffuser, but I can't through that in for free because of what they cost new. The cylinder I have is about 5 inches in dia. and about 16 inches tall not counting the valve height into that. Just let me know if you are interested.
Matt