The lighting seems a little low for HC, especially since it is a plant requiring high light. Also I would start dosing the water column, since with your set up you are making your plants grow very quickly and they need the right nutrients to build healthy leaf structures. Another question though, how do the plants look when you get them?
Another thing that I want to mention is that the water is a little warm. I'd dial back the temp to 76, only do it slowly.
Good luck. First thing I would do is turn down the temp. Then see what happens, since everything else involves buying stuff.