I have heard of adding Epsom salt to the water for constipation (usually Bettas and the fat body types of Goldfish). I would do this in a hospital tank, not treat your display tank. 1-3 tsp per 5 gallons. If your Angel is used to low GH I would start with 1 tsp/5 gallons. Next day add another, then the 3rd tsp the next day. If he is already in hard water then go ahead with 3 tsp/5 gal.