Bro, be advice tt keep marine fishes at low specific gravity, will do no good for the internal organ itself. Take for example, fish from red sea SG is1.025-27, Brazil area 1.025, s.e.asia 1.023. They will not be able to generate enough minaral in and out their body. At 1.013, you need to monitor the PH closely. 40 days of low sg is enough to kill off all parasite on their body. My advice bring back to at least 1.020 slowly if all your fish is ok.