A lovely and upright, perennial form of cool season collard greens, the tree collard can live for up to 20 years, depending on the variety. Grown in a sunny window, after the trunk of your tree collard becomes established, it produces tons of leaves that can be harvested yearround though are reportedly sweeter if given some winter frost. Perhaps simply running the air conditioner during the summer will give you the opposite effect, sweetening your perennial collard leaves inside your home or office. 

As sweet potatoes are actually part of the root system of a robust, vining plant, to grow them as part of your riparium fish tank filter will require a lot of space. This is no issue if you have a large tank, though, if your aquarium is on the smaller side, some creativity and dedication can help you to create a semi-hydroponic sweet potato filter for your fish tank. 

Of course, if you're not all that interested in growing sweet potatoes, you could simply use the sweet potato itself to filter the water and then replace it ever so often. 

I've found that it is quite difficult to drown asparagus which I am also growing in the wetland area of a duck pond with amazing results. 

Asparagus will grow very well in a moderately sunny window, create an amazing root system that will fill up any semi-hydroponic system beautifully, and produce wonderful, organically grown asparagus spears, assuming you don't add anything fishy to your fish tank. 

As bamboo has been used for waste water treatment for human people, it is more than adequate to help balance your fish tank with its large rhizomes and amazing, neverending growth. The bamboo rhizome takes well to being grown in leca clay balls, though this is definitely a plant that, once large and established, will have you topping off the water in your fish tank quite regularly, if given good sunlight. 

Bamboo shoots are edible though, if you're not interested in doing that, you could always leave the shoots to harden into culms and then harvest them for your crafts or as support poles for your vining plants.