Looking for alittle advise on a 90G planted tank I am setting up. Alittle about the tank..flourite substrate and I have 4x54w of T5Ho available for lighting and am planning on a fairly heavy plant load. It comes down to this...CO2 or excel as a carbon source and the catch is I work out of town numerous times in the summer for up to a month at a time. I would love to have the growth and beauty of a co2 tank, but is it possibl to leave it unattended for 30 days at a time? (Gf will be there in case of emergency, but knows nothing about aquariums!!) Could this work if i used a fert doser or 2 maybe, one for macro and one for trace? could it work with 4 weeks between water changes ? Or would it be better off going with excel and hoping the tank will turn out ok. Thanks alot!