You can but you risk killing the bacteria and cycling your tank which can wipe out the fish if not on top of daily water changes. If the fin rot is not bad you could bump up the temp to the low 80's and do daily water changes and vacuuming for a week and see if there is an improvement. At the end of a week with NO improvement you would need to medicate IMO. Fin rot is a secondary infection caused by damage to the fin by mechanical or other fish infliction. The infection can happen due to water condition not being so great. Sometimes these infections can be prevented by weekly vacuuming and water changes or, sometimes you just have a fish with weak immunity. Good luck with you Jewel!!