I have 5 Pseudotropheus socolofi (1m/4f) in a 40 gallon tank. One of them swims up and down, just never stops. Except to eat. Water conditions are perfect. Plenty of caves and hidding spots. They are all very young about 1-1 1/2 inches long. The other fish are all fine. This one just won't stop swimming mostly in one corner, up and down really fast. Its one of the females and they have been in the tank about two weeks.