50ppm is a lot of co2, 30ppm is the usual recommended amount for tanks with livestock, but as already mentioned, your mileage may vary.
As far as ferts go, if Coursair was talking about API leaf zone, it's not much of a fertilizer, it only contains potassium and iron. Flourish comprehensive is a much better alternative, unless you are ready to start going with dry ferts of course. It's a good choice if you are deficient in one or both of those things but it definitely doesn't cover the list of micros/macros that plants utilize.
