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I couldn't make up my mind whether this topic should go here or in Planted Aquaria. Since it's part plant topic, part general filtration topic. So I thought I'd put it here. Mods feel free to relocate

Everyone is (or certainly should be!) aware of the existence of bacteria that convert nitrogenous wastes, via multiple steps, into nitrates, which are of course a premier plant fertiliser, as anyone with an algae problem will only too happily testify! But, I've encountered an aritcle in Practical Fishkeeping which explains that higher plants can form the basis of an entity called a Vegetable Filter, which will take the nitrogen cycle several steps further, and as a beneficial side effect, remove a host of other unwanted compounds from freshwater aquaria too.

Effectively, this is a freshwater version of the marine aquarist's algae scrubber - the refugium with Caulerpa macroalgae and certain mangrove habitiat plants that has been used by some marine aquarists for numerous years. The big difference here is that the key organisms are higher plants.

The article was written by Peter Bradley, who maintains 20 different aquarium set-ups, with a wide range of pH and hardness parameters for different fish species, and in all of them, floating plants and certain other key species play a part. Their principal role initially was that of algae control - reducing both available light for the algae, and available nutrients. Duckweed is a prime example of a floating plant that reproduces at an astonishing rate, and which uses its roots to abosrb nutrients directly from the water. However, that is, as Bradley says, not their only role. Those tiny root systems are intricately branched and feathered, and provide a place where bacterial colonies can thrive - yes, the very same bacteria that we strive to cultivate in our biological filters. But around the Duckweed roots, they thrive because the Duckweed roots effectively force-feed the bacteria with oxygen. As an ammonia and nitrite removal system, it is pretty effective!

Then, Bradley mentions Amazon Frogbit. This plant again is an aggressive coloniser in the wrong places, but in the aquarium, where it can be controlled, it has a secondary use as an algae magnet. Again, the roots provide a colonisation point for bacteria, but in this case, the bacteria also create conditions that green algae like. The algae then preferentially grow on the Amazon Frogbit's roots, and can be harvested at regular intervals.

Bradley cites the usefulness of floating and certain submerged plants with an account of his office aquarium, which was an expensive, high-tech full Dennerle set-up with a mass of gadgetry. The office suffered a weekend power outage lasting 48 hours, and Bradley only found out about it on the Monday morning. He was expecting a total wipe-out, but to his surprise, there were no losses. There were fish gulping at the surface, but that was because the water was stagnant, and surface gas exchange had been further reduced by the floating plants. Ammonia and nitrite levels were significantly lower than anticipated, and the Phyllanthus fluitans floating plants in the aquarium had gone into overdrive once the ammonia levels began to rise. They were effectively hoovering the ammonia out of the water, almost as fast as the fishes could produce it, and in the process, launched into a growth spurt of such proportions that Bradley had to remove three bags full of surplys Phyllanthus from the aquarium!

Bradley then cites a book that should be required reading for aquarists everywhere - Ecology Of The Planted Aquarium by Diana Walstad (sadly, he neglects to provide his readers with an ISBN number - a woeful omission!). Quotes from this book are used to illustrate certain points, for example about the ability of floating plants to remove metals, whose toxic actions are described in some detail. Several of Bradley's favourite floating plants, however, remove these metals, and can do so very efficiently, while seemingly coming to no harm themselves. One particularly resistant species is Water Hyacinth, which in the wrong places is a pest (Florida residents will doubtless know all about this!), but in the aquarium is a copper magnet par excellence. Water Hyacinth has been demonstrated in the laboratory to remove virtually all the copper from a concentrated copper solution in 14 days, without suffering any damage itself, so imagine how useful it would be as a copper remover in the aquarium!

Water Lettuce, Pistia stratiotes, obtains its carbon dioxide from the air, and thus does not have to compete with the algae in the aquarium. Bradley's quote from Diana Walstad's book is apposite here:

Emerging plants exhibit much faster growth, more efficient use of carbon dioxide, light, and more efficient oxidation of the root area enhances biological activity in the root masses. Hygrophyla polysperma grows four times faster when grown in the air and when floating needs to photosynthesise ten times faster than submerged leaves.

As if to reinforce my own point about observing one's aquarium in action, Bradley then quotes an Angelfish breeder of his acquaintance, as saying that in fry tanks containing Hornwort (Ceratophyllum demersum), fry mortality and the need for water changes was reduced.

Then, Bradley outlines a water purification system based upon a sump containing floating plants. The idea is to construct a partitioned aquarium (he cites one of 36" x 8" x 8", but sizes could be changed to suit different set-ups), through which water is slowly circulated from the main aquarium. This sump is lit overhead, like a normal aquarium, and the different chambers are populated with different plant species. One chamber uses Water Hyacinth (toxin removal, especially heavy metals), another uses Hornwort (nitrate removal, ammonia and algae suppression) along with Amazon Frogbit (algae control), and a third chamber uses Phyllanthus fluitans to control ammonia. Another chamber could contain a peat bed - this would increase the efficiency of any carbon dioxide injection system used to boost plant growth, by adding dissolved organics to the water that not only mop up heavy metals, but also create the perfect 'blackwater' conditons for breeding Cardinal Tetras, for example. A small amount of leaf litter and fish waste in the sump is actually desirable, as it provides the plants with 'booster' nutrients, including various important elements such as iron that the fish excrete, which of course increases the photosynthetic efficiency of the plants. Moreover, growing plants require a certain amount of protection as they grow, and the dissolved organics provide this - removing them using activated carbon filtration would defeat the purpose of the vegetable filter, and should only be required in dire emergencies.

And, as a bonus, I've hit upon an idea that Bradley missed in his article! As this vegetable filter only has a modest current flowing through it, it would be ideal as a fry nursery. No other fishes trying to eat the fry, plus all those floating plants providing root systems seething with biological activity, a natural home for infusorians. Use some judiciously positioned fine mesh netting to prevent the fry being sucked into the inlet pipe of the return pump, and let the fry grow inside their plant-filled nursery free from harm. The slow (but sufficient for gas exchange) current could also provide a hatching and rearing facility for Gammarus shrimps, Daphnia, freshwater copepods such as Cyclops (beloved of German aquarists as a fish food in particular), and no doubt a host of other useful organisms intended either as fish food or as aquarium maintenance organisms. With a soft river sand substrate with rounded granules, or a peat substrate, one of the chambers would make a superb Corydoras nursery, and the thought that your vegetable filter is also helping to nurture 25 baby Panda Corys is surely a wonderful incentive to build one and try it out!

Needless to say, once I've got space to let fly with this idea, and the money for the additional equipment, I'm going to fire up a vegetable filter the first chance I get. Imagine a sump that not only doubles your aquarium capacity, acting as an extension to the biological filter, but also acts as a fry nursery for your baby Corys, Tetras and Dwarf Cichlids, and provides a place for you to accelerate the growth of small plants before transferring them to the main aquarium, allowing you to cultivate that 'underwater Dutch garden' look. I like this idea a lot!



[span class="edited"][Edited by Calilasseia 2004-07-17 08:50][/span]

Panda Catfish fan and keeper/breeder since Christmas 2002

good article calla. I have noticed that all of my tanks are much cleaner with live plants.

Really? I've found just the opposite! I can't seem to rid my tanks of decaying plant matter! My tanks were perfectly clean before.

The freshwater sump idea is interesting, but I have a problem with it. A sump-type filter would have too much water turbulance, therefore outgassing too much of my precious co2 which I am injecting with a pressurized setup. I would lean more towards a refugium type setup for those plants...in a segmented refugium. My tanks are heavily planted and I have no need for any of that on them, but I do have a 55 gallon that has insufficient lighting for most plants where it would be nice to have a refugium or sump that was lit seperately ( easier to light in a cheap manner....one cheap light would provide enough for a sump or refugium, whereas it would take more $$ for the whole tank), to get the benefits of the plants without having to plant, maintain, and light an entire tank.

When the power goes out, I don't worry about my planted tanks too much. I haven't had 48 hour outages, but on 12 and 24 hour outages, I don't get so much as a single fish gasping for air, whereas on nonplanted I have to run a battery operated air stone.

Nice thread, Calilasseia.

ingnious. great article calla. might have to try that one day... when i have spare money to buy the parts.

Nice to know I've provoked some thought with this one!

Needless to say, again, funds allowing, I'll be giving this one a test ...

Panda Catfish fan and keeper/breeder since Christmas 2002