Larger individuals in small groups tend to be bossy and often dictates the 'pecking order' during feeding time leaving smaller individuals starving. Increasing their number to avoid constant picking on one target and adding tall plants to block lone of sight and give others a chance to eat maybe...
Unfortunately most of the available freshwater 'eels' are too large even for your tanks. You could go for with a wide assortment of readily available eel-like loach species though
Try using activated carbon with your filtration, do a 25% partial water change and change your feeding routine to a once a day feeding or every other day routine.
Like others also said, animals don't just stink. I keep roaches as feeders and even those don't stink
or a small group of rasboras or danios does well in shallow tanks as well but make sure to have the tank covered well since they sometimes jump when excited or stimulated during feeding time :D
Americans are not as gullible as the people here when it comes to uncommon animals. You can paint a turtle white and sell it off for a hundred dollars here under shady labels like snow turtle or ice tortoise hahahaha -__-
Also 2 males for any anabantoid species in the same tank is like asking for a pacman-mayweather fight.
I second byron's recommendation for warm water. The most crucial water element they need. Too bad for other fishes, warm water spells fungus growth.
There is a reason why this fish is...