Put a background on it. The fact you can see throught the tank is distracting your eye. With a background your attention will be focused on what is happening inside the tank rather than whats on the other side.
You can get patterned ones or plain colours. I have a plant themed one on mine. Although I will probably be changing it to a plain black one in the neer future.
A background will be much better and it will make the fish feel more secure having abit of enclosure so to speak! Maybe somemore plants or rocks? I'd do the background first and u will b amazed by how much different it feels!