Excel alone can be done easy enough.

I suggest one of those DIY CO2 internal reactors I described how to make.
Make one, add DIY CO2 to that, add light etc/nutrients, change the brew weekly, you will have no issues with CO2 on a 20 gal tank.

They are very effective for DIY CO2 and designed around that source, but also work very well with canned cO2 as well.


Regards,
Tom Barr