You don't want to be adding salt to tanks with Corydoras and flying foxes unless they have a disease. Salt can cause heart and kidney problems and kill softwater fishes like Corydoras if they are exposed to it for too long.
Water softeners on taps usually swap calcium chloride for sodium chloride (salt) and this could be causing a buildup in the fish.
You need to stop adding salt to the aquarium and depending on how hard the well water is, either get a reverse osmosis (r/o) unit to remove the minerals and then mix some well water with some r/o water to get a correct hardness for the fish. Or use rain water or distilled water to mix with well water for the correct hardness.
---------------------
If you are using well water, you shouldn't need to add a water conditioner because there shouldn't be any chlorine/ chloramine in the well water. Some water conditioners might bind heavy metals and that might be useful until you get the well water checked, but if there is nothing bad in the well water, then it doesn't need any water conditioner.
---------------------
If this problems started after you did a water change, there might be something contaminating the well water.
Have you had the well water tested for anything and everything?
You can do basic ammonia, nitrite, nitrate, pH, GH & KH on the well water with normal aquarium test kits. But there could be toxic chemicals contaminating the well from surrounding areas.
You need the well water tested by a water testing company to find out what is in it.
Water softeners on taps usually swap calcium chloride for sodium chloride (salt) and this could be causing a buildup in the fish.
You need to stop adding salt to the aquarium and depending on how hard the well water is, either get a reverse osmosis (r/o) unit to remove the minerals and then mix some well water with some r/o water to get a correct hardness for the fish. Or use rain water or distilled water to mix with well water for the correct hardness.
---------------------
If you are using well water, you shouldn't need to add a water conditioner because there shouldn't be any chlorine/ chloramine in the well water. Some water conditioners might bind heavy metals and that might be useful until you get the well water checked, but if there is nothing bad in the well water, then it doesn't need any water conditioner.
---------------------
If this problems started after you did a water change, there might be something contaminating the well water.
Have you had the well water tested for anything and everything?
You can do basic ammonia, nitrite, nitrate, pH, GH & KH on the well water with normal aquarium test kits. But there could be toxic chemicals contaminating the well from surrounding areas.
You need the well water tested by a water testing company to find out what is in it.
