How do these 2 types of oaks differ? Are they both suitable for Zone 7a?
Northern red oaks (Quercus rubra) are native to Eastern U.S., have good fall color, and are at home in a variety of habitats. Hardy in zones 5-9. Southern red oaks (Quercus falcata) are native to eastern and central U.S. and are usually found on dry slopes and ridges. Hardy in zones 6-9.
This article will give you a general idea of the care requirements for Red Oaks (common name Northern Red Oak): https://www.gardeningknowhow.com/ornamental/trees/oak/red-oak-tree-information.htm
I live in Tamaulipas, Mexico. The weather is hot most of the time, and we used to have a few cold fronts.
Although this tree can produce some red leaves in the fall, the term "red" primarily refers to the wood.
It may be that your tree isn't happy with the soil. The red oak needs full sun and acidic, well-drained sandy loam soil. High pH soils can cause chlorosis.
I've pasted a link to an extension article, as well as one of our own.
My best suggestion, however, is to contact a local agricultural extension office for a soil test.