Right. Choose if you are doing a high-tech (pressurized Co2) or low-tech (no pressurized Co2) tank first. Go from there. You can do either, same rules apply (balance fish load=plant load=Co2=light=fertilizers), just low tech and high tech tanks have different %'s on the rule sets (low tech, less ferts, less light, less Co2). Also less water changes on low tech. There's a sub-forum for Low Tech tanks. Most folks here do EI (estimate index) and high-tech, more gadgets ($), both have benefits.
And yah, $25 for a bag of Eco won't buy you pressurized Co2, so probably better off going Low tech and getting the Eco and just read up in the low tech forum on the different ways to do those tanks instead of the high tech tanks that most people here do.
Oh, and but LOTS AND LOTS of (stem) plants to start with to *try* and fend off algae problems
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