Im still not convinced there is any real major problem. Good news, I see that you're getting some side branches starting, cool!! You're on the way to getting some clones. As for the curling, it may not be heat but maybe they are just being sensitive to the light spectrum from your T5 bulbs.. back them off 6 inches. It isnt gonna hurt and will encourage the side branches to stretch out for light and you want the side branches anyway for clones right?
If you are still super concerned about how they look lets check a few things out:
1, Make sure your PH meter is calibrated, or check your nutrient solution with PH drops to validate.
2, Make sure your PPM/TDS meter is calibrated ok using calibration solution.
3, Check nutrient strength in EC mode on your meter, what is it?
4, Are you shaking the nutrient bottles before mixing solution? They should be shaken well....
5, Are you mixing nutrients in the correct order? Some nutrients need to have each part added in a defined order.
6, Are nutrients being mixed in the reservoir of water or are you mixing concentrated nutrients? Don't mix concentrated nutrients.
7, How are you adding PH down when needed? Are you ensuring the roots are not being exposed to raw PH down?
I would say that if the above are all in check, you shouldn't have anything to worry about... Imperfections happen, plus it could even be genetic, not knowing what is being grown you don't have a baseline for the strain behavior.