Now I'm wondering about a CO2 system. How much do they cost and which
ones to think about installing for a 65 gallon tank. What is this DIY
CO2 system everyone talks about?

http://www.dlink.org/aqua/CO2.html

If you want you can replace the needle valve with Clippard or other needle
valves.

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Thank You

Dominic
http://www.dlink.org/aqua