I am fairly new to Rose gardening and have one hybrid tea rose (Chihuly) right

Baking powder is the wrong stuff, and a whole lot more expensive than
baking soda. A pound will set you back less than $1.

Blackspot is a fungal disease, worse during warm humid weather. The
spores are pretty ubiquitous. It tends to be worse on stressed plants,
and plants in pots are almost by definition, stressed.

Your choices are a regular program of spraying and sanitation, learning
to live with blackspot, or choosing disease resistant cultivars

American Rose Society has chapters all over:
http://www.ars.org/Districts/districts.htm, and there is also a Houston
Rose Society. A&M maintains a list of very disease resistant roses:
http://www.houstonrose.org/earthkin.htm -- you may find one there
you like better and is a whole lot easier to grow for a beginner.

Kay