Veggie Filters

[RTR]

It is generally accepted that healthy plants have a beneficial effect on the water conditions in fish tanks. They absorb dissolved minerals, including some metabolic waste products, from the water and from the mulm in the substrate. They convert these into plant mass. During their lighted period they adsorb carbon dioxide (CO2), produce oxygen (O2) and release that into the water. If the water is not oxygen-saturated, there is no visible evidence of this. In saturated conditions, very small bubbles of O2 will form at the leaf surface and be released - this is the “pearling” plant tank growers point to with pride as evidence of strong healthy metabolism in the plants. In the dark they do use oxygen from the water (and release carbon dioxide), but they do not use as much as they produced in the prior light period. So if we accept all that, it is reasonable to want to have plants in our tanks, not just for aesthetic enhancement, but for the benefits they can provide to the water quality and thus to our fish.

Some tanks, however, just are not compatible with heavy planting, or even with planting at all. Have you ever tried to keep plants with an Oscar beyond half-grown? Or Uaru? Or a Scat? Many fish either by behavior (Oscars and many Cichlids, most very large fish) or by being herbivorous (i.e., plant eaters, such as Uaru, Pacus, Scats, and goldfish, along with many, many others) are incompatible with many plants. Larger Puffers may not eat plants as standard diet, but will likely damage them by biting holes in the leaves while gathering snails, or Oscar-like, just because they do not want them in the way. Such fish may also consider plant-cleaning crews such as snails, shrimp, sucker-mouth catfishes, and Siamese Algae Eaters as either potential enemies to be chased from the territory, or simply as a sushi appetizer.

Such tanks can still have the benefits of being planted, even without having plants in the tank at all. Have you ever heard of the concept of a refugium? In short, this is merely providing a refuge where the plants (or whatever) can live, separate from the display specimen and thus are protected by this separation, but with water exchange between the two areas. There can be several benefits here - not only having the positive effects of healthy plants on the water, but also simply by increasing the water volume.

There are commercially available algal scrubbers that may provide similar function, but I have no personal experience with these units. I have done DIY algal “filters” for marine tanks, where the function was very much like that provided by vegetable filters in freshwater tanks. Walter H. Adey and Karen Loveland, in “Dynamic Aquaria”, Academic Press, 1991, advocate such techniques as scrubbers and refugia for maintaining water quality.

Physical Setup and Circulation:

The simplest refuge for freshwater plants is just adding another tank, with water exchange between the two. The arrangement I have used most often has taken advantage of those commercial tank stands holding one tank at normal seated viewing level, and a second tank (usually of the same footprint but lesser height) below it. It is this arrangement that I will discuss as an example, but many others are possible.

If you have a 55-gallon display housing a near-adult Oscar or other large omnivorous specimen, plants are out of the question. Filtration by a suitably sized canister or similar equipment can guarantee undetectable ammonia and nitrites. Despite regular routine maintenance by gravel vacuuming and partial water changes along with filter cleaning, the tank’s nitrate level may be higher than desirable for long-term maintenance. You could perhaps most easily double the water change schedule and offer much cleaner water that way, but this may not fit your schedule of free time available. You can benefit by the use of a vegetable filter in the lower tank. A 33XL (48” x 13” x 12”) happens to fit well beneath a standard 55 on several of my stands, so this is the tank selected for this example (Endnote 1). In addition to the upper tank’s regular filtration, add an overflow siphon/surface skimmer such as is used with wet/dry (W/D) filters, or a Vortex constant-level siphon set. These units maintain a near-constant water level in the tank on which they are installed. Regular siphons will not work in this application. They would drain the upper tank and overflow the lower tank. These W/D overflow units skim off the water surface layer and move the skimmed water outside the tank by siphon(s). The Vortex unit does not skim the surface. Outside the tank the unit incorporates a standpipe (adjustable in the Vortex), commonly prefiltered by a sponge (not in the Vortex, but it may be added if kept clean by frequent rinsing), to drop water to a lower level. Some overflows are crenellated, that is, they have squared notches around the skimmer rim. Others have smooth flat rims. I see little functional difference between the two overflow types. They maintain the water level at least at the level of the overflow rim or the standpipe. When additional water is pumped into the tank from a sump, the water level rises to overflow (hence the name) into the unit. The steady state operation with water being pumped into the tank will have a level very slightly above the rim of the overflow or standpipe.

The output from the upper tank overflow is directed into the lower tank, arranged so that the output does not blast into the substrate, if the veggie filter uses any substrate, especially an enriched substrate. My commonest technique is to plumb the display tank output with PVC pipe, feeding the output into a horizontal section of PVC or CPVC pipe in the refugium. That horizontal pipe is capped on the end and drilled with holes along it’s length, or is made up of a series of tee-fittings joined as a manifold. The last is my preferred option, but the former option is used in shrimp-containing refugia. This pipe can be mounted either just above the substrate along the back or end of the tank, or below the water level of the lower tank, say two inches below the inner rim. In either case, the holes in this DIY (do-it-yourself) “spray-bar” are aimed horizontally forward (toward the front or opposite end of the tank) to promote circulation.

Return from the lower tank to the upper uses any reliable powerhead or pump which will work without excessive noise against the “head” of the system. “Head” is simply the vertical height difference between the water levels in the two tanks. In the paired tank system in this example the head measures 32” with the stand and tanks I am using. For this example, an AquaClear Model 50 (formerly 402) powerhead is sufficient for low-flow applications; a Model 70 (formerly 802) would provide more turnovers for a high-flow setup. Several different sized Eheim ‘Hobby Pumps’ have been similarly used for return pumps. Please remember that the rated volume of the powerhead or other pump is determined at zero head and zero resistance, so is a theoretical maximum. In actual application we will fit the pump with a prefilter sponge (which offers some resistance to flow) and be pumping against a 32” head through tubing or pipe with bends. Rated output of this pump (AC 50) is listed as 270 US gallons per hour (gph). Actual measured output with sponge and head and pipe and/or tubing resistance is down to approximately 100 gph measured volume, or only a bit over one total tank volume turnover per hour. Flexible tubing (Eheim seems to hold its flexibility well and resists crimping for me) carries the output to the upper tank. The top of the tubing is fitted with a return fitting which instead of the usual inverted U-shape offers another bend, to release the water return horizontally just below the tank surface. The return is best set with the release just barely below the operating water level of the display. In the event of power loss, air would be sucked into the tube to stop back siphoning. Some of my applications are hard-plumbed with PVC/CPVC (usually 1/2” ID for this size setup or smaller, larger and high-flow setups would use larger tubing). Release to the display tank from these involves a couple of 45-degree elbows, usually not cemented but simply pressure fitted so that the final horizontal water release is partly open to the air both under power and power-off circumstances. If another type of return is used with release below the water level, it should have a hole drilled just below the operating water level. The hole is a siphon break. In the case of power or pump failure, water would start back siphoning from the upper tank to the lower. Having the hole drilled above the power-off water level will introduce air to stop the siphon during power-off conditions. If the siphon break is below the overflow rim level, this siphon break will determine the volume drained down to the lower tank in power-off conditions. During setup, this component should be tested repeatedly. It is a critical component in overflow or flood avoidance. In operation, the return should be kept clean by brushing it externally and internally. Allowing the siphon break hole to clog will lead to disaster and flood. I never rely on one-way valves for power-off or pump failure protection. They suffer from failure all too often themselves.

Designing and tuning your own system will depend upon tank sizes and the pump chosen. In any case, in the event of a power outage or pump failure, the maximum water level in the lower tank must be set low enough to absorb the difference between the upper tank level with the pump on and the level with the pump off. With the overflow I have in place, this difference is just about 3/8” in the upper tank, about 1/2” in the lower. The positive meniscus in the upper tank, compared to the negative meniscus in the lower tank produce the small observed difference. This level is marked on the glass of the lower tank with a tape line. I also mark the normal (lower) operating level with the pump running. When topping up the system during pump operation, this latter (lower) level is the guide. If topping up with the pump off, the higher line is used. Filling the lower tank above the proper level could result in overflow during any power failure. This too is critical to the operation of the system. You must allow for drain-down under power-off conditions. This is also the benefit of having the second, lower tank as close as possible to the same footprint as the upper. It is certainly possible to use a smaller tank below the display, but the change in water level between power-on and power-off will be magnified by a factor roughly equal to difference in the surface area of the two tanks. In this example, if a 15 gallon had been selected, its change in level from powered to power-off would be more than twice as large from the approximately 48x13” to the 24x12” tank.


Now that we have see some of the reasoning behind the use of a plant refuge or vegetable filter, and some detail of a typical setup that I have used in several systems. Now we’ll look at the sort of options for planting that have been used, and some variant layouts. I’ll give some maintenance hints as well, and a summary of the concept.

Multiple options are available for the plants in the vegetable filter itself. The selection made will depend on your experience level with plants and what you want from the system. The easiest and simplest option is to use floating plants in the lower tank. In this format, you need no substrate. Just purchase a few bunches of floating plants such as tropical hornwort or Anacharis (Endnote 2), remove any rubber bands or weights, and let them float freely in the tank. These floaters may also be anchored to the walls by suction cups with attached threads wrapped loosely near the base of the plant stems. In my experience, two 40-watt broad-spectrum tubes will serve nicely. If your display houses a “Big Nasty” fish, it might be a good idea to have the heater or heaters for the whole system located in the veggie filter as well. Lighting should be on timers. The largest benefit to the system will have the veggie filter on reversed light cycle from the display tank. That is, if you have the display on from noon to midnight, set the timer for the veggie filter for 11:30 PM to 11:30 AM. Light “on” time and the number of tubes used may need modification by the plant type chosen. If you use shorter "on" times, leave the dark period at the end of the veggie filter's light cycle. that is when oxygenation is at or near its peak From this the veggie filter will be doing its job and providing additional oxygen to the display tank during its’ dark cycle. Even if there is no planting in the display tank, the reversed light cycle seems to favor the least change in pH during the veggie filter’s light cycle (Endnote 3). If there are some plants in the main tank, having both tanks lighted at the same time will magnify the daily pH swing. That is not a significant issue, but bothers some folks. Obviously in some settings, a lighted tank would be undesirable during the night. It would not be a good system in a regularly used bedroom. One of my systems operating in this fashion is in a room that serves occasionally as a guest room. Black-painted cardboard or light plywood was kept in a nearby closet to cover the front of the veggie filter when guests are in residence. Now there is cellular black shade which can be lowered to cover the opening of the stand to serve the same purpose. The back of that tank is in the adjacent room, so does not contribute light to the sleeping area.

I have some experience with growing plants, so I usually have an enriched substrate and rooted plants in the veggie filter. If you select low growing, propagation by runner type plants such as pygmy chain sword or dwarf sag, or smallish Crypts such as wendtii, you will get fairly rapid increase in plants (depending on the plant, Crypts are slower) and usually the excess can be traded in to your local fish store (LFS) for credit. Once the veggie filter and the plants are established and stable (several months), you could even add a pair of Ancistrus or Peckoltia catfish and harvest babies periodically. Some floating plant cover may be needed for the Crypts. A few, not a solid cover, of the bunch/stem plants can serve for this, or any of the small floating plants such as duckweed. Duckweed or Riccia can be a pest, but when controlled by frequent harvest (by netting much of it out for composting, or feeding to herbivorous fish such as goldfish or mbuna), it too serves nicely as a water purifier. I do not recommend the plant most commonly used for water purification, water hyacinth, for tank growing. It is IME (in my experience) difficult to grow indoors under artificial light, but this may be an artifact of my relatively low nitrate levels. Plants selected need to be ones that you can grow rapidly and/or easily under the conditions selected, so they will absorb material from the water. Unhealthy plants will increase water problems, not reduce them. Supplements of trace elements may be needed in the water column, but this varies with the individual system.

Emersed Growth Systems:

In this setup, the plant's roots are submerged, while the stems and leaves are in the air. This technique allows the plants access to room air and in particular carbon dioxide, which may be in short supply in aquarium water. Insufficient CO2 is the commonest limiting factor in submerged plant growth. Several families of aquatics grow in nature either immersed (Endnote 4) or emersed (Endnote 5), dependent upon the seasonal water level in the stream, lake, or bog. Commonly they show different foliage in the two conditions and require some adjustment time during the change from one to other. For our purposes however, it may be far better (easier) to use houseplants rather than aquatics. Emersed growth plants seem to extract more minerals and metabolites from the water than the submerged plants (with the possible exception of Anacharis, which is a real nutrient sponge). My favorite plant for such use currently is Crinum americanum, the Florida Swamp Lily (Endnote 6), but it is not suited to use in a tank beneath the display due to its size and height. I use plain aquarium gravel, not enriched for this plant. The bulbs increase by offsets (pups) near the mother, or by runners ending in pups at a few to several inches separation from the mother. This particular plant is fairly light hungry, 2 each 40W NO tubes being about the minimum for me, 4 each 40W tubes are better. Historically I have reset these plants every other year. I have recently found that allowing unchecked growth for four years was a mistake. The original just over 2” of gravel became over 6” of gravel and masses of live roots. Division required heavy Felco pruners to isolate the individual or mother and small pups from one another. The take-home lesson here is to not neglect pruning and division of your veggie filters.

I have used two different setups for emersed growth veggie filters. One employs the same arrangement as the submerged growth system discussed previously. The veggie filter is below or behind the display tank. In the simplest format, a grid of plastic “eggcrate” (a light diffusion grid work that looks like a three-dimensional graph paper grid, available from hardware stores or lighting supply stores) is supported on short sections of 1 1/2” ID PVC pipe resting horizontally on the bare tank bottom. One corner of the grid is notched out to provide space for the return pump and a float switch. The float switch should be one that will shut off the pump if the water level drops to or below the pump intake level. This will avoid the possibility of burnout of the pump. Water from the main tank is released into the area below the grid at the opposite end of the tank from the return pump. The water level is set at or just above the grid. Multiple cuttings of Pothos are pushed into the grid with the cut ends at the tank bottom in the water between the bottom glass and the grid, the foliage in the air. The same two each 40 watt tubes are used as in the earlier system. The Pothos will grow quite rapidly and need regular harvest. A number of different common houseplants will grow well in this setup, but should be selected for plants that will not grow too tall for the restricted height of this tank. Spathiphyllum has been recommended for this use, and it works well, but it would need a much taller tank, or one not below the display tank. Canoe Plant, or Moses-in-a-boat (Rheo discolor), also has worked in such a setup. It is much shorter than Spathiphyllum and thus less demanding of height. Cover glasses are not used with this setup, and due to the increased exchange with room air, there is more evaporation of water from the system. This setup requires daily topping up for me, due to the relatively small water volume in the veggie filter.

An alternate arrangement is a tank or tray above, beside, or behind the display tank, with the water level above that of the main tank. Gravel-filled pots (or pots with bottom half gravel, top half long-grain sphagnum moss, not ground peat) with plants set in the tray with lighting suspended above them. Water is pumped via powerhead from the display tank into one end of the tray and overflows by a spillway (similar to that on hang-on power filters) or by standpipe back into the display tank. Other than DIY epoxy-coated or commercial fiberglass trays (including some wallpaper trays or window boxes), I have also employed Aquarium Systems’ Gemini or System 2 filter housings for this. In this setup, the empty filter housing sits directly on the tank, and much smaller pumps are used than those suggested for standard filtration with these units. Plants such as Spathiphyllum, grown in gravel in recycled grocery store berry baskets in fiberglass trays seem to do quite well in these setups, and even provide long-lasting blooms (spathes) above the tank. The suspended lights above the plants are kept on the same cycle as the tank for this system. Note that emersed plants do not significantly contribute oxygen to the water. Also note that with the veggie filter tray above the display tank, the display itself is the drain-down tank in the event of power failure. To avoid having the water level in the tank visible below the rim during normal operation, I make the plant tray substantially smaller than the display tank. This reduces the display tank change in water level during power “off” situations.

Maintenance:

The addition of a veggie filter in no way removes the requirement for regular water changes, vacuuming, etc. It supplements those tasks. It increases the nominal volume of the system by the addition of the second tank, and unless used for breeding small suckermouth cats it does not add significantly to the system fish load. This does mean less pollution build up per unit volume between partial water changes. This is not just or only the plant removal of material, but also by dilution from the increased water volume. In the example used in Part 1 of this article, the system was nominally 55 gallons. It now is a nominal 88 gallons. Dilution alone should improve the water conditions, as it has reduced the bioload. If before a one-third partial was done weekly, just over 18 gallons was removed and replaced; now the partial will need to be about 29 gallons for the same percentage change.

Floating stem plants will need to be harvested regularly. Remove the oldest portions to discard, keeping the newer parts. Rooted plants will need to be thinned out periodically. Again select the older, larger plants for removal (this time as trade goods, not discards) and keep the younger, more vigorously growing plants in the filter. This sort of division tends to cloud the water temporarily, so I do this work with the exchange pump off. Usually I only disturb and replant only about 1/4 to 1/3 of the planted substrate tank in one session - this minimizes the disturbance to the filter function. Such substrate-based veggie filters are excellent grow-out tanks for baby sword plants. Just be sure to remove them for trade-in before they become too large for the veggie filter. Emersed plants such as Spathiphyllum will need to have younger plantlets pulled off the mother clump and replanted or given away. For this plant I keep the larger plants for flower production. Pothos I tend to decimate by scissors, replacing some old growth with younger cuttings.

I do usually have snails in a veggie filter, Malaysian Trumpet Snails (MTS) in a planted-substrate tank, ramshorns in bare tanks of floating plants or in the water portion of emersed plantings. In immersed growth tanks, ghost, Amano, or other algae eating shrimp may be needed for assistance in algae control, or either Siamese Algae Eaters or small suckermouth catfishes. Algae control in this system is more to keep the plants healthy and growing strongly more than for aesthetics. These setups are also prime breeding refuges for such easy shrimp as Red Cherry shrimp.

Algae itself could be used to remove nutrients from the water, but removing algae is to me much more work and far less pleasant than keeping the higher plants in check.

Always rinse the prefilter sponge(s) intake on the return pump frequently. I recommend weekly rinses at the least. Exact scheduling of such tasks is setup-dependent, so the user has to decide on the interval. Removing trapped debris before heterotrophic bacteria have digested it is a good water management practice in any tank.

Summary:

You can employ plants to improve your water quality, even if you keep fish that are incompatible with plants. It just requires a bit of ingenuity and juggling on your part. A bit of DIY is required, but no advanced techniques are needed. There are many variations on the ideas presented here, and the refugium concept has application beyond the use of plants. Refugia also have been used to house daphnia to control green water or bacterial cloudiness. My first FW experience with that technique was based on Pet Library’s “Advanced Aquarist Guide” by Feroze N. Ghadially, London, 1969. I believe that book is long out of print, but it may still be available in some libraries. My first algae bed filter was SW, and even earlier. This is not something new in the world.

One of the variations on the theme is how the overflow or constant-level siphon in arranged. There are several ways to achieve the same end, some of which are less intrusive in appearance, but a bit heavier in the DIY aspect. Wet/Dry type skimmer/overflows have some disadvantages- they require the use of feeding rings if any floating food is used (Endnote 7). Big advantages are that overflows do not allow any surface film to form on the display tank and they are available commercially.

Constant-level siphons may also be a DIY project if you can work with PVC tubing or pipe. The detail is beyond the scope of this note, but not particularly difficult.

Exactly what level of water exchange between the tanks is “best” is one of the unknowns you will be facing. These systems are not common. They do work, but as with all plant tanks, each system is individual to some degree. Generalizations are still difficult. In the example used for the first description, substituting a 40-long tank (for the 33XL) carpeted with crypts and a few floaters could probably use a lower exchange rate. The same 40-long with Val or young Amazon swords might or might not be able to use a third light, but the same higher exchange rate as used for the free-floating stem plants.

When you change any given component, it is going to affect the rest of the system. The same 40-long with rotala, hygro, or similar hungry, fast-growing stem plants might need a third tube, or compact fluorescents, or at least improved reflectors, or perhaps a forth tube, or CO2 supplement, or both to maximize nutrient uptake, and could possibly need macronutrient supplements as well as micronutrient dosing. So the selection you make will depend in part on the job you need to do. Overkill is a very real possibility here. Setting a veggie filter that requires weekly or biweekly pruning, high light, and CO2 could very well be swatting a gnat with a bulldozer if the original problem was of relatively small scale. Try to set a system that will simplify your life, not complicate it. Playing with gadgets and tanks is entirely too much fun, IME. I have been guilty more than once of building a Rolls Royce when I needed a wheelbarrow.

Currently I have been experimenting with constant lighting on some FW planted refugia. I had done this previously for planted Daphnia refugia with good results, so I am trying similar practice with the plant-only refugia. The lighting on these tests is similar to the examples above, but a two-tube tank has only one tube on at a time for 12 hours, then the other. Some test tanks have used only a single tube on 24/7 (the more efficient use of the equipment). To date the best results are given by Vallisneria spiralis or Hygrophila difformis. These tests are very much works in progress, so long-term conclusions would be premature. Note that there is no net increase in power usage in this format, and that the effects of constant lighting on inverts (snails and shrimp) are still in very early stages, but no issues have turned up so far.

Very low nitrate tanks are possible with heavy planting, as is clean, highly oxygenated water, even when the display specimen is incompatible with plants. All you have to do is set a planted refugium, preferably without flooding your home. Hopefully you will be able to do this in a way that will lessen your routine workload and increase your pleasure and satisfaction with your fish, at the same time improving the fish’s living conditions and hopefully prolonging its life. This is definitely a win-win situation.

Endnotes:

Endnote 1. Other combinations have used similar stands, commercial or DIY or custom, including: 75 over 40 (but note different footprint size), 50 over 30 Breeder, 40-long over 33XL, 29 over 20-long, and 20 over 15. I have also used comparable setups with much larger volumes, but only using custom stands. I have a multi-tank circulating range (3 each 40-long, 3 each 30-long, one 20-high, one custom 30, plus the veggie filters) which uses 2 each 20-longs as veggie filters. One is lighted with the majority of the range, the other with reversed light cycle.

Endnote 2. Anacharis is more correctly known as Egeria densa, but also may be called Elodea densa. Most LFS list the plant as Anacharis. There are several near but cold-water relatives which are not as desirable in tropical tanks.

For more complete discussion on the real plant and its relatives, see:

Elodea

Endnote 3. During active photosynthesis, submerged plants take in dissolved CO2 from the water. This results in an increase in the tank pH due to lower CO2 and its associated carbonic acid.

Endnote 4. Immersed growth refers to growth underwater, i.e., below the water surface.

Endnote 5. Emersed growth refers to growth above the water surface, i.e., on or above the water.

Endnote 6. A mature emersed Crinum is about three feet tall, with a comparable but not solid spread, and weighs several pounds. It is a large plant at tank scales without question.

Endnote 7. Homemade feeding rings are easily made by use of a length of airline tubing joined into a circle by a tubing connector. Customize to suit your fancy by the length of tubing used.

Any questions or comments I will attempt to answer on the boards.

[zanzimog]

Great article, very thorough. Perfect timing.

[zanzimog]

I was thinking about setting up my veggie filter half emersed and half immersed, maybe with a bed of val. Am I asking for trouble, in that the two parts would work at cross purposes and just give me an algae bog?

[RTR]

I'm confused - Val does not grow emerse SFAIK, and generally wants a decent depth of water.

[zanzimog]

Sorry, wasn't clear. The val would be in the submerged section, with a plant to be named later, maybe a mix including a smaller crinum species, in the emersed section.

[RTR]

IME, such planting would likely be better separated by type. Any emersed planting with enough vigor to be useful will shade out adjacent submersed plantings.

[zanzimog]

SOunds like it's just better to keep it straightforward. Thanks!