I didn't notice if your tank is heated...unless I overlooked it. That can cause a big problem if household temperatures fluctuate regularly. I recently added heater to my goldfish tanks because I use a programmable thermostat that lowers the house temp during the day. The tank temperatures fluctuated as much as 5 degrees (or less) during a 24 hour period. The fish were listless on the bottom of the tank and their fins developed large tears. Added a heater and no more problems. I was amazed at how damaging daily temperature changes were to goldfish which otherwise do fine in cooler temperatures.