Photo: Red Mangrove tree in the plant filter.
One aspect of our hatchery systems we use to raise fish that always seems to fascinate hobbyists when I speak at fish clubs is our plant filtration system. Goliad Farms exclusively uses plant filtration designed by us through trial and error. We have no carbon or mechanical filters. For a detailed description of our plant filtration, see the article by Charles Clapsaddle in April 2010 issue of Tropical Fish Hobbyist magazine, “Plant Filtration—No Water Changes.”
Our plant filters in our two large greenhouses (about 3,000 square feet each) consist of three main stages. Our smaller greenhouse (about 1,500 square feet) uses the plant filter in one of the two larger greenhouses. Below is a description of the two large greenhouse plant filtration systems.
First Stage: The first filtration stage uses plants in the vats. Our plants of choice for this stage are hornwort (Ceratophyllum demersum), a rootless floating plant, and guppy grass (Najas guadalupensis) that we stock in most of our vats. Both are rapidly growing plants that do not suffer a significant slowdown in growth during the winter. With hornwort, we keep a ten to twenty inch sprig with new growing tips in each vat. About once a week, the sprig is pulled out and the older end pruned and discarded. Guppy grass doesn’t float and is used sparingly since it will fill a vat from bottom up, interfering with feeding and netting. In addition to the hornwort and guppy grass, there is a group of volunteer plants often present in the vats. The group includes several species of algae (mat and hair algae primarily) and duckweed (Lemna). We don’t encourage these plants, especially the duckweed, because it interferes with feeding and netting, but they are present and almost impossible to eradicate. These plants feed heavily on the ammonia waste products of the fish.
Second Stage: The second filtration stage is a complex of plants in our floor gutter. This complex consists of hornwort, algae, Bacopa caroliniana and duckweed. Again the algae and duckweed are volunteers that we don’t particularly encourage but tolerate out of necessity. Bacopa is a native plant with an emersed growth pattern. It forms floating mats and grows up on to our wooden walkways. Its primary deficit is a tendency to go into dormancy in the winter and ceasing to grow. The floor gutter in each large greenhouse is thirty by eighty feet in area and averages six inches deep. It is walled on three sides and is dammed at the open end by a thirty foot long, six inch high wall. The water falls over this wall into the plant filter.
Third Stage: Third and final stage of filtration is a sump at one end of each greenhouse. This sump is about thirty by seven feet in area and several feet deep. The sump is populated with Red and Black Mangroves and Oja Santa. Mangroves produce thick, fleshy leaves that require heavy feeding by the plant on the fish wastes in the system. Oja Santa is a member of the pepper family (Piper), which grows rapidly and produces large leaves used in Central American cuisine.
We tested another plant, Dieffenbachia, but soon considered it a failure not because it didn’t work for filtration but because it has a toxic to human skin sap. If you are interested in it, here’s a blog I wrote about it: http://goliadfarms.com/monster-plant-dieffenbachia-species/.
Collectively, the three stages of plant filtration maintain zero levels of ammonia, nitrate, and nitrate in the system and provide us with an addition source of revenue in the form of plant sales.