Listless fish

[CJ29DJ]

I am having a "problem" with my fish being practically listless. I have 3 South American Cichlids (Green Terror, Firemouth, Convict) in a 55 gal. The fish are not full grown and still relatively small in comparison to their full growth size. I got them in the summer and they showed a lot of activity and movement around the tank and were eager for food. Now, the Convict shows a decent amount of movement while the others typically sit near the bottom of the tank by the heater (although the fish have always been swimming at the bottom of the tank in and out of my multiple rock caves). The tank's temp is at 80 degrees. I have checked for ammonia levels and they are at 0. I have tested the pH and it's at around 7.0. I do 25% water changes every two weeks and feed the fish once or twice a day. I'm wondering if moving the landscape might help. Otherwise, I'm stumped. Any help or information would be appreciated.

 

[garfy]

I would recommend doing 50% water changes weekly to keep your Nitrate levels at a reasonable level.Below 20 if possible.
Do you know what your Nitrate and Nitrite levels are?