Do you keep gravel in it? It is easily boiled and offers a lot of surface for good guy bacteria. Dumping a little really funky gravel in the garbage will not bankrupt most of us.

What about a little Najas or hornwort? The latter is very sensitive to many medicinal dyes. But both plants are such inexpensive, fast growers, given half a chance, that if the plants lived in the medicinal tank, it would offer shelter, comfort and maybe use up some ammonia. If it dies, it can be removed with routine water changes before it becomes a problem as an oxygen sponge. For the fry, it would give them grazing surfaces and again maybe help with ammonia and if the lights are on a lot, provide some O2.

Of course when I need a quarantine tank, the one I have set up looks so great (though I haven't been clever enough to grow out fry there) that I pull another tank out of dry dock, toss some gravel from an established tank in and add the Najas. ;)