DIY
I am using a Hagen Nutrifin DIY Co2 system, and a seperate baking powder & vinegar system. Both were rated for 40gal, and my tank is 65gal.
I use the aqueon 55/75 HOB filter, and a 100 whisperer air pump for my sand fall.
My Co2 tester is a darker blueish green, and never the medium tone green...