Hey!
Add more balls, you shouldn't be seeing the water bubbling.
After doing that check you air pump and make sure there's good intake.
The plant looks droopy and tips are curling as if it were over watered in soil.
Given that your roots are in water this could be a simple lack of oxygen flow in the water.
Also there wasn't any nutrient information.
Make sure to add that information so we can better help you.
Water PH should be 5.5-6
Looking at the pictures I saw a few tiny brown spots, that could be the beginning of calcium Deficiency. keep an eye on that.
Hope this helped, Good luck and happy growing!