I have a method for feeding these frogs reptomin effectively. I will admit it's strange.
Anywho this is how I feed my frogs reptomin. I mix it with PE Mysis Shrimp (PE is the brand, feel free to substitute but PE is considered the best quality). Mysis shrimp are small crustaceans, pretty much freshwater brine shrimp.
I take a tiny bowl that I do not use soap on and put the frozen cube of mysis shrimp in it, add some tank water and let it thaw. I drain most of the water out, then add some reptomin and let it get a little soggy. I then just squeeze it into a clump and hand feed it to my frogs. They go pretty crazy for it. The mysis gives the reptomin a really appealing smell to them and all things considered mysis shrimp is pretty good food for a growing small frog.
I still use the same method today even though my frogs are quite large, I just make bigger reptomin clumps. My frogs are terrible at eating reptomin by itself, they have a lot of trouble finding it I never just drop pellets in. It just creates too much of a mess.
Any mysis left over I just feed to my fish, who also love the stuff.
P.S. Your plants probably need more light, 68F is fine for the frog and the vast majority of plants. You may want to try Java Fern and Anubias if your light is inadequate to grow other plants. It's that or upgrade the lights.