It wont prevent the plant from growing, maybe slow its growth. It depends mostly on your stock. Do they have enough DO or do you need to supply more. Java takes nutrients up through its leaves, it requires some water movement in order to supply the plant with fresh nutrients effectively. A bubbler could create sufficient current. Java fern is a very hardy plant and will grow under most conditions, I wouldnt worry too much unless you plan on planting more demanding plants. GL