Just a thought, but did you have any live plants in Jack's tank? If not, that might be something to try in the future. Of course, they don't replace the need for regular water changes (as I'm sure you do anyways :) ) but they do act as a biological filter and help to keep ammonia at a minimum. I just ordered a bunch of the little moss balls- they came in a pack of 5 for about $6 including shipping, on eBay. Which works, because I have 4 bettas and one more on the way! But in my experience with other plants (Betta Bulbs from Petco, which work great) they do keep the ammonia level down.