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Low-Tech Planted Discus Tank

Jean Opsomer (opsomer-at-iastate.edu) [address updated 4/99]

The purpose of this illustrated write-up is to demonstrate that it is possible (and not that difficult) to have a well-planted tank without having to resort to complex and expensive equipment and products like CO2 injection, undergravel heating cables and Dupla fertilizers. I'm going to briefly describe my aquarium set-up and my ``method'' (or lack thereof) for achieving healthy plant growth. If, after reading it, you have any questions, don't hesitate to send me an E-mail at opsomer-at-orie.cornell.edu. First, for the sceptics, here are some pictures of my plant tank: The tank is a 70G with an Eheim 2215 cannister hooked up to reverse-flow undergravel filter. The filter material is mainly biological substrate, with some carbon and floss on top. The filter intake is covered by a prefilter. Light is provided by 2 40W Triton bulbs and 1 40W (cheap) cool-white, turned on for 12 hours/day. Gravel is relatively fine (2mm diameter), layered about 3" thick, without additives mixed in. The water temperature is kept between 78-82F and has pH around 7.0. The (total) hardness is 60-80ppm. Phosphate levels are not detectable and nitrates are somewhere between 10 and 20ppm.

The animal inhabitants are 2 full-grown discus, 2 farlowella (twig) catfish, 1 yoyo loach (Botia lohachata, to keep the snails in check), 15 Rasbora heteromorpha and a healthy population of Malaysian burrowing snails. The plants are (in rough order of quantity in the tank): Valisneria spiralis, Hygrophila polysperma and difformis, Cryptocoryne affinis (?), Echinodorus amazonicus and osiris (swords) , Microsorium pteropus (java fern), Anubias barteri (?), Bacopa caroliniana, Didiplis diandra. The question marks indicate the ones where I'm not completely sure of the species. In the past, I've also had good luck with Ceratopteris thalictroides (water sprite, submerged), Aponogeton crispus and Egeria densa, but have never been able to keep any of the fine-leaved plants (cabomba, etc...) for more than a couple of months. Same goes for Ludwigia repens and Hygrophila corymbosa.

This current set-up and inhabitants have been together and stable for about 2 years, which is the last time I did a major overhaul/cleaning. Before that, the tank had been running for another two years with similar plant growth. During all that time, there's been virtually no algae present in the tank (except when going away for extended periods), and I have not purchased or added a single plant since the overhaul.

To achieve low-tech plant growth, I follow a few guiding principles: (1) keep fish density low to avoid build-up of NOx AND/OR phosphates (note the or); (2) only keep plants that are compatible with the tank; (3) provide plenty of light; (4) perform large weekly water changes; and (5) use small (!) amounts of iron and trace element supplements.

Let's go through each of those in a little more detail.

I used or in (1) to indicate that as long as ONE of the nutrients for plants (and algae!) is in short supply, the most efficient organism will prevail in the tank. In my case, there's no algae in the tank although the nitrates are at the relatively high level of 10-20ppm, while the phosphate level is not detectable. As one can tell from the list of fish species in the tank, it indeed has a light fish load. It used to have 2 more discus and a school of corydoras until one year ago, with the same plant growth and lack of algae, so it is possible to have a higher fish load than the one I currently have and still maintain a healthy tank. What is the maximum? I don't know, but by monitoring the water quality and performing sufficiently large water changes (more on that below), one can most likely achieve the level of ``fish vs. effort'' that is optimal for one's particular tastes...

One of the mistakes I used to make is insist on having one or two large pl*cos in the tank ``to keep down the algae.'' While these fish indeed chew their way through most kinds of algae, they produce so much waste that I invariably ended up with clogged, dirty gravel and worse water quality than if there had not been pl*cos present. The twig catfish are a nice compromise, since they are so small (even though very long!) that they do not produce a noticeable accumulation of waste materials.

When the next one of my guidelines mentions compatible plants, I mean that not all plants will grow in each tank, because of water chemistry, temperature, size of tank, etc... The current species choice is the result of a selection over time: I've tried just about every plant that seemed remotely compatible at least once, and if it didn't thrive, I did not insist but instead switched to others. It is probably no coincidence that the species list above contains lots of ``easy'' plants... Unlike true aquatic gardeners, my goal was to create a pleasing green environment, not to grow ``challenging'' new plant species.

As far as lighting goes, I already mentioned that I have 120W of fluorescent light on this tank, which is turned on for 12 hours each day. As I'm sure will be true for most people, a special hood was required in order to increase the amount of light in the tank. I bought a double-strip, reflective hood and use it in combination with an old single-strip hood. Triton bulbs, while expensive, produce much more light and last for several years without noticeable decrease in light quality. Clearly, there are other brands that would perform just as well. See the excellent George Booth postings for in-depth reviews of the quality and quantity of light from the different fluorescent lights on the market.

The amount of water changed depends on what is required to keep your water parameters fairly stable. If not enough water is replaced, the nitrates and phosphates go up, the pH drops and ``scum'' forms on the surface. If too much water is changed,... never mind, I don't think there is such a thing as ``too much'' in this case (as long as the new water is properly conditioned in terms of pH, temperature, etc...!). Personally, I test for nitrate concentration and try to keep it below 20ppm. I usually change 15-20G of water (20-30 percent) weekly. Since my tap water has pH 8.4 and hardness 200ppm (not everybody is lucky enough to have aquarium water stream out of the tap...), I use a reverse osmosis filter and mix the water 60/40 tap/RO. With this mix, I thought I would get aquarium water with a total hardness around 120ppm. Whenever I test it, the values are lower, around 60-80ppm. I'm assuming that the plants somehow take up some the calcium, which would explain the difference.

Some people might argue that an RO unit is not exactly low-tech. True, but depending on the chemistry of your tap water, you might not need it and still be able to grow plants following the principles outlined in this write-up. In my case, it was a choice between purchasing the RO unit or being limited to African cichlids...

In the past, I have used Wimex Ferroplant and Trace Element as plant supplements, but 6 months ago I switched to Kent Marine's Discus Trace Elements and Freshwater Plant Supplement, superior products I think. Both are easily available through mail order and cost about the same as the Tetra products. I add 1 1/2 tsp of the Discus Trace and 3 tsp Plant Supplement with every weekly water change. I decrease both quantities proportionately for a few weeks whenever I see a beginning of green algae appearing on the leaves of plants.

Since I've already described most of my maintenance schedule, here's the rest of it: when taking out water every week, I siphon the gravel in the area where the fish are fed. I also rinse out the sponge from the prefilter. The only thing left to do for the weekly maintenance is to trim back the most rapidly growing plants: valisneria runners, hygrophila shoots and java ferns. Every 3-4 months, I prune back more vigorously, clean the cannister filter and push a few Aquarium Products laterite balls (cheap!) under the roots of the cryptos and the amazon swords, who seem to enjoy a somewhat richer substrate than the straight gravel.

Once a plant tank is running smoothly, it is relatively easy to keep in good health. The really hard part, however, is getting a newly established tank to reach this equilibrium state. Here is a path to follow, which I used when I overhauled the tank two years ago. After cleaning all components (except the filter media, of course) and thoroughly rinsing the gravel, I refill the tank and reroot all the plants. I also reseed the gravel with the burrowing snails. They are very good at eating any leftover food, even in tight corners where the fish can't get to it, and they seem to do a great job of turning over the gravel, thereby avoiding compaction of the substrate. For the plants that require it, I bury laterite balls under the roots as mentioned before. Since I started off with a working biological filter (in the cannister), I also put all the fish in at this stage. If you don't have that luxury, you need to get your nitrogen cycle going first, which I'm not going to describe here...

At this stage, it is a good idea to emphasize quickly growing plants such as Hygrophila difformis and polysperma. I also put in floating plants (Salvinia auriculata and water sprite), which grow VERY quickly and do an excellent job of preventing algae from growing on the submerged plants by blocking the light and soaking up excess nutrients. While Valisneria also grows and propagates very quickly, it seems to take longer to ``get started,'' so I don't recommend it as one of the starter plants. This choice of plants will speed up the process of achieving a tank where plants out-compete the algae.

Now, here's a little secret: while the tank is all frazzled from this big overhaul and the plants are trying to figure out what happened, it is the most likely period for algae to take over the tank, right? Once they do and begin smothering the plants, the balance tips in the algae's favor and... we all know the rest. So, in order to avoid that, I put a phosphate-absorbing resin in the cannister filter. This temporarily keeps the phosphates very low and keeps the algae under control. When the plant growth finally picks up speed, they continue to use up all the available phosphates and soon overtake the algae as nutrient uptakers. I use Sea-Chem's PhosGuard, which is somewhat expensive but not too bad in large packages. I went a little overboard and bought a 2-pound box 4 years ago, and I've only barely made a dent in it... I leave the resin until the first (or second) cannister filter clean-up, then stop putting it in.

After 2-3 months, if everything is going well, I begin removing some of the fast-growing Hygrophila and most of the floating plants, let the Valisneria take over more of the tank and put in the slower-growing Amazon swords, Cryptocorynes, Anubias. For another 3-4 months, I'm extra-careful in monitoring any drifts in water quality and algae build-up, which I correct by increasing the water changes and reducing the amount of plant supplements added. After that, the environment should be stable and you can finally enjoy your plant tank as well as make friends at your favorite petshop and/or aquarium club by bringing them free plants when you visit them...

Jean Opsomer
(html translation by E.O.)
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This page was last updated 28 April 1999