Since we use plant filters as our only means of filtration and water purification we are constantly searching for and testing plants that will thrive in our system. For those who subscribe to Tropical Fish Hobbyist magazine, I wrote an article about our system; please see “Plant Filtration—No Water Changes,” TFH April 2010.
When we originally developed the system we were in Santa Fe, New Mexico, where our well water came up at 53°F and being at 7,000 feet the climate is generally cold, so large water changes weren’t an option. In order to conserve warm water we implemented a recirculating system wherein all the water flowed through a large plant filter (10’ x 25’ and about 2 feet deep) before returning to the tanks. The plant filter was stocked with water hyacinth (Eichhoria crassipes), which is a floating plant that sends out horizontal stalks where new plant crowns grow. It is a very heavy user of nitrogen in the form of ammonia and it kept our ammonia levels at zero. Unfortunately, Texas, our current home, considers it an invasive exotic and has made it illegal to possess. Ever since we’ve been casting about for the perfect replacement.
We’ve tried red mangroves (Rhizophora mangle) and black mangrove (Avicennia germinans) and both have been successful in controlling ammonia and preventing the growth of single cell algae (green water) in our sun lit greenhouses. But we are always testing other plants. By accident I tested what has become our “Monster Plant.”
My mother had a small Dieffenbachia bowmannii (at least I think it is that species) that her cats had kept shredded and barely alive. I rescued it and placed it on the edge of the gutter in our cichlid greenhouse. Water from a nearby vat’s overflow splashed on to it so I didn’t need to remember to water it. After a few months it had grown into a very large multi-trunked plant about four feet tall. Also, I found that it managed to grow around and cut off a water valve. It’s roots had spread out into the water as well. It needed to be moved, so I chopped off the trunks and dropped each one between rows of 55 gallon vats.
Now, it’s important to realize this plant causes severe dermatitis when its sap comes into contact with bare skin. I definitely realized it that night when my arms itched intensely. Some cortisone cream fixed the itching.
Fast forward a few months. The damn plant was taking over.
The stems (actually trunks about 4 inches in diameter) were pushing the vats out of alignment, pushing pipes into our way, and clogging up overflows. Something had to be done. So, we are carefully removing the plant. (Ask Ashley, a hatchery technician, what happens when you aren’t careful; in her case a systemic reaction complete with hives everywhere.) In some ways it’s an ideal plant filter plant. It grows rapidly and uses up ammonia, but I think it would need to be placed in a large shallow tank where it could grow without interfering with operations. But, then how would you prune and cull it when it overgrew its container? At least with water hyacinth you could safely handle it and throw surplus plant into our Red Litter-worm beds.
Live and learn…