I'd try emptying out the water and letting the soil dry off, then watering from the top with a dilute seaweed fertiliser. Dump the water that filters through into the reservoir a couple of times and keep watering the soil itself for a while to help to flush out any nasty things built up in the soil. If the damage is not too bad it should recover, but if it is not showing good new growth in a week or two then you might need to go with new soil.