If you don't have a heater then regulate your lights. Make sure that they aren't on all the time. If that doesn't work then do you have it in sunlight? If it is in the sunlight then you need to move it because you will have green water very soon.
75 Gallon-Oscar, Jack Dempsey, Green Terror, 2 Fire Mouths, 2 Black fin sharks, common pleco, Sail fin mollie
54 Gallon Corner-Yellow lab, Albino red fin zebra, Auratus, Blood Parrot, common pleco
30 Gallon-Mollie, 3 Balloon Mollies, Angelic Loach, 2 Kuhli Loaches, angel-ram hybrid, 2 cory cats, tiger clown pleco, Common pleco