This amount of PO4 works well, I've found errors with some calculators, I do my own. I would rather folks stick to the teaspoons as they make the entire process much easier and are fine, 1.5-3.0 ppm is fine for error for PO4.

You can get away with less water changes with the slower growth from Excel, but not do away with water changes completely like non CO2/non Excel methods.

I get good color in my non CO2 tanks though.
You can also use the ADA AS, or a sand cap and organic soil and/or manure that's been boiled or soaked for 3 weeks etc.

All these and the water column dosing method work well, you will have more nutrients to grow a non CO2/non Excel tank in well this way, but it's not required.

Main thing is when you top off the water, add some KNO3/KH2PO4/Gh booster and traces in(weekly or once every 2 weeks etc).

Also lightingm, you can grow most plants in non CO2 tanks with 1 w/gal of T5 and similar light with PC's provided a good spread of light(T5's are better here).

Example:
A 55 gal tank and 54 w T5 with good reflector.
A 20 gal with a 24" 24w T5 with good relfector etc.........

You will still gain from CO2 at these levels even.
Or you can opt for no CO2/Excel at all.

Regards,
Tom Barr