I will leave the plants as is. I am going to clean my collander (whitething) this weekend and try some quilt batting if still dirty. I can see the bottom but it is not nearly as clear as it once was. Should I go ahead and rinse the filter media in my biofilter?

Not sure what is meant by 'good companion plants'. Since neither is much troubled by diseases or pests there isn't any protective effect to consider. And since rhubarb stays put for a decade at least and garlic needs to be planted annually in well cultivated ground I would have thought they were actually very poor companions. My two plants cover an area about 6 feet across and the leaves kill off anything growing beneath them. In my view rhubarb needs a dedicated space to itself and the garlic belongs in the vegetable garden.

Datura doesn't poison the soil any more than their cousins, tomatoes and eggplants do. You can plant anything there, but if you let it go to seed, you may still get some seedlings up.

I would give it a try, catherinet. It couldn't hurt.