If it's fish only going down quickly won't stress them. Going up quickly does. Their internal sg is 1.008. They just won't need to drink as much or process out as much concentrated salts in th lower sg. Inverts are a different story though. So if you have snails ,shrimp etc they won't like th lower sg.
To go from 1.027 to 1.025 is about an 8% change . So replacing 2.3 gallons of salt water with 2.3 gallons of ro water should do it.That should have no effect on the biofilter. Even much larger drops will only cause only a small short lived supression in bacterial activity.
I keep my seahorse fry tanks at around 1.024 to 1.025 and 74 to 75 degrees There are peppermint shrimp in the filtration area for clean up of excess food ,breeding and contributing some larvae to the food chain and they do ok at those sgs but might not do well at 1.022. The adults thrive in 1.026 to 1.027 at about 77/78 degrees and breed regulary in their tank. They would do just as well Isuspect in lower sg but that tank is plumbed int my reefsytem and natural seawater sg avaerages 1.0264 in any case. Not sure keeping lower serves a useful purpose.