Humm..............you are not suppose to do water changes in a Non CO2 method.
So the water you start with should not matter much if at all.

Likewise, the CO2 method allows the soft vs hard issue to go away because you are adding CO2..........

So in both cases this is not an issue due to tap.
If you do frequent water changes on a non CO2 tank, I would expect plant and algae issues.

Yes, you had 2x as much light as you should on the non CO2 tank, that was doomed before you started.

So you need to decide which method you want to do, the CO2 method will increase the growth rates by 10 fold.

Each method has it's trade offs.
EI is not for non CO2 methods, see the articles tab in the forum here for more about that.

Regards,
Tom Barr