You may have answered your question. You stated they are
growing quickly. Shell curling is a result of that. Are
you feeding the sticks daily because I think that may be alot
for 2 little turtles. How big are yours right now? Shell
length? You also could lower their water temp to about
74-76 degrees. Too warm temps could cause rapid growth.
As long as you have a proper basking area they will be fine
with a little cooler temperatures. In the wild they regulate
their body temps and no where do they live in a constant high
70's degree water temp. Just try to duplicate how they live in the wild. The wider range of temps the better.

Linda