The bloat is caused by bacteria. Quite a number of fishkeepers (myself included) have been successful in curing bloat as follows:
-Major water change (50%) to start.
-Remove carbon/resins from the filter.
-Add a tablespoon of salt per gallon of water.
-Treat with Metronidazole 250mg per 20gal. Also known as Flagyl.
-Leave the system alone for 3 days and don't feed.
-On the 3dr day, do a 30-40% water change and retreat with Metronidazole at full dosage. Replace the salt.
-Leave the system alone for 3 days. Don't feed.
-The bloat should be visibly reducing by now.
-One the 3rd day, Do a 30-40% water change. Again, retreat and replace salt.
-If the bloat looks well on it's way out, offer a light feeding.
-On the 3rd day, same routine. Begin feeding regularly in smaller than usual portions.
-After the 3rd day, water change and salt. If the bloat looks to be gone skip remedicating.
-Go back to business as usual.
Monitor the feeders you offer the knife for signs of illness. The bloat comes in more often with the feeders than with newly introduced tankmates.
I use a 4 bin rotation for my feeder shiners (1000per bin). Each batch is quarantined/monitored/treated for 3 weeks before feeding out to my predators.