The macro nutrients are wells erved with harder water, it's the trace metals that are mostly the issue.

Yes, you can add more, but often that does not seem to help, still, CO2/macros will get you a long long way.

So then it's just an issue with traces and namely the chelator that works best for hard and/or soft tap water.

the Texas water is got a lot of CaCO3, and that's what adds lots of the Ca and KH.
So for GH, all that you might need might be Mg really.

Epsom salt is very cheap.
You can add Epsom salt to the traces also(the CMS + B etc)
Then dose both at the same time.
TMG would be better for your tap water though.

Regards,
Tom Barr