Hello Richard203, I am a tech support agent from Seachem Laboratories. We typically recommend treating sunken belly using MetroPlex (http://www.seachem.com/Products/product_pages/MetroPlex.html). A sunken belly could be an indication of internal parasites. However, if you decide to use MetroPlex in a medicated food mix, you can find the recipe and the dosing instructions on the provided link. I hope this could you!