Until their gut clears. Depends on the situation as to how long. In 45 yrs in the hobby I have only dealt with intestinal bloat or blockages about 3-4 times. Unfortunately by the time it’s noticed you’re looking at about 80% mortality.
When I dose for moving my tropheus around I keep it at that concentration for a week. If they’re eating & pooping well internet wash out with my regular water changes. If not, I keep it at that concentration even with water changes until they’re eating & popping well.
Epsom salt indefinitely will not harm your fish. Some keepers of African cichlids add it as a maintenance dose.
It would still help to know what you’re keeping. It provides a better context for answers
