I think normally it's 1tsp for 5 gallon, but I believe gouramis aren't too happy with salt so maybe 1tsp for your ten gallon and watch. Be sure to dissolve it in a cup of water and pour it in the tank that way. Again I'm not the best at remembering quantities, I usually search through posts for what others say. You could try posting in the fish health board and they might be able to give better advice.