AQUATIC HORTICULTURE
BY KAREN RANDALL

The Aging Substrate

With time, the nutritional value of even a soil substrate will decline. It is up to the aquarist, at that point, to decide whether to try to increase the nutritional value by adding solid nutrient sources to the substrate, or whether it is easier just to take the tank down, replace the entire substrate and replant. Most aquatic gardeners find that they can get at least three years out of a soil substrate without outside intervention.

Sooner or later, whether a tank is set up with a soil substrate, a laterite substrate or something else, the aquarist will find that the entire substrate is becoming rootbound. In a tank with modest growth, it could take three years to reach this point. In a tank with very fast growth, it could happen in as little as 18 months. It is easy to test for this problem by digging your fingers down through the substrate in various locations. You should, in most places, be able to get your finger down to the glass with a minimum of effort. If the substrate is so choked with roots that you can’t get your fingers through, it is time to take remedial action!

KAREN RANDALL
For the experienced aquatic gardener, working with soil substrates, such as that used in this lovely tank, can be very rewarding if you are aware of, and can avoid, the possible pitfalls.
Of course, you could take the tank down and start over, and, if you have a soil-based substrate, that may be your best option. If you have chosen a laterite-based substrate, there is a less drastic solution. Mentally divide your tank into quarters. Over a period of months, remove the plants from one section at a time. Thoroughly vacuum the gravel in that section. Yes, you’ll lose a little laterite, but lots will be left behind. Go through the plants you removed. You’ll most likely realize that there are too many to put back in the same space! Divide the root balls as you would a terrestrial garden perennial, with a sharp knife. Replant a reasonable number of plants and sell or give the rest of them away. Depending on the quality of the laterite you used originally, the water will remain cloudy from a few hours to a day or two, but it will eventually clear.

In three months do the next section, and so on, until the whole tank has been done. You’ll be amazed at the vigor with which the plants in the rejuvenated sections grow! Just as with terrestrial plants, aquatic plants do not grow well when they are over crowded.

Substrate Heating/Circulation Systems

Let me say at the outset that it is entirely possible to have a beautiful, long-lasting aquatic garden without any form of substrate heating or circulation other than what is provided by the plants themselves. This is the last place you should spend your money. If finances are of any concern at all, spend your money first on really good lighting, then on a good, reliable supplemental CO2 system. Only then, if you still have money burning a hole in your pocket, is it time to invest in substrate heating devices.

There are three functions of substrate heating/circulation systems in the planted tank. The first, and most important, is to re-supply trace elements to the substrate for use by root-feeding plants. As mentioned before, a side benefit of this function is that it also tends to trap phosphate in the substrate, where it can be used by the plants, but not by algae in the tank.

Second, a delicate balance must be found between providing enough oxygen to the substrate, but not too much. Too little oxygen can lead to the buildup of poisonous gasses. At the same time, mildly anaerobic conditions lead to a reducing environment where trace elements are available in a form more easily used by the plants. While it is possible to cause severe anaerobic conditions in the substrate, particularly while playing around with unconventional substrate media, in actual practice it hardly ever happens.

In a heavily planted tank, the roots of the plants spread quickly through all areas of the substrate. As they pull nutrient-laden water into their tissues, water from above drops down to take its place. At the same time, the plants themselves bring oxygen down into the substrate, preventing dangerously anaerobic conditions. Granted, this happens quite slowly, but it does seem to be enough that most aquatic gardeners are never faced with seriously anaerobic conditions in the substrate.

Still, a system that gently moves water through the substrate may keep a better, more constant supply of nutrients and oxygen available to the plant roots. This is particularly beneficial in the first few months after tank setup, when the plants have not yet fully extended their root systems. It also appears to be beneficial on the other end of tank life, where it seems to be able to considerably extend the useful life of the substrate. These benefits will be more apparent in tanks with a gravel/laterite substrate than in those tanks with a soil-based substrate.

Finally, if a way can be found to integrate the temperature of the substrate with the rest of the tank, most plants find it beneficial. Some sources feel that it is preferable for the substrate to be slightly warmer than the water above, while others feel the important thing is that the substrate not be allowed to become substantially cooler to avoid stratification of the warmer and cooler layers. In the absence of a substrate heating/circulation system, it can be very beneficial to insulate the bottom of the tank with styrofoam sheeting (found at either building supply sources or craft stores) to avoid heat loss. Another option is to use the heat of lights on a tank below to warm the tank above.

For those who are not yet convinced that it is possible to maintain a healthy tank with the use of an undergravel filter, this is your chance. While it is entirely possible to provide all the biological filtration needed for a planted tank (or any other tank for that matter) without resorting to an undergravel filter, the undergravel filter plate can be used effectively in a planted tank. The key is to make sure that the flow rate is very gentle. This could be accomplished with air lifts, but air-driven undergravel filters have the disadvantage of driving off necessary CO2 in the tank. If a tank has a good enough CO2 concentration, air lifts set at a very low rate may be acceptable, particularly with less-sensitive species. Very small, variable-flow powerheads are another option that may be able to provide a slow enough flow through the substrate.

A simple and very effective solution that I have used is to drop a small 7.5-watt, non-thermostatic submersible heater down each uplift tube. This provides a very slow water current in the uplift tubes, which moves water very gently through the substrate. If you want to use a small-size gravel that would fall through the slits in an undergravel filter plate, the plate can be wrapped in fiberglass screening before placing it in the bottom of the tank.

Of course, there is also the option of going with a commercially available cable heating system. These are available from at least two companies, are complete and ready to use, and are very reliable. They work by heating the area just above each cable, while leaving cooler spaces in between. The theory is that warm water rises above the cables, while cooler water from above drops in between the cables to take its place, creating gentle convection currents through the substrate. This theoretical action is very hard to prove or disprove because of the many variables involved. Suffice it to say that whether these currents are actually created, or whether it is simply the benefit of the warm substrate, this method has a proven track record for helping produce and maintain beautiful tanks. The one drawback is that it’s very expensive.

Various plans are available to make your own cable heating system. This is a very inexpensive alternative for those who are mechanically inclined. From what I have read, these home-made systems can be put together very reasonably.

Some people have tried using reptile heating pads or water bed heating pads attached to the underside of the tank. While this may work, and some people have been satisfied with this method, it is risky. There have been reports of people cracking the bottoms of their tanks this way.

From time to time, other variations on the substrate heating/circulation theme are introduced by various inventive souls. As long as the end result is very slow, even circulation and heating, the system should work.

Set Up

Regardless of whether you use a substrate heating system or not, or what substances you intend to use as nutrient sources in your substrate, the set up of the substrate itself is similar. Obviously, if you are installing a heating system, that goes on the bottom of the tank. Dampen one-third to one-half of the gravel. There is no need to thoroughly rinse this layer unless there is a lot of organic debris mixed in with it. If your gravel comes from a commercial source, there shouldn’t be.

The laterite or other substrate additives should be mixed thoroughly into this layer. Spread it evenly over the floor of the tank. Rinse the remaining gravel very carefully, a small amount at a time, under running water. The cleaner you get this top layer, the less initial cloudiness you’ll have in your tank. Spread this very clean gravel carefully over the bottom layer, making sure that you have at least 1 inch of clean gravel over at least 2 inches of amended gravel.

Be very careful when filling the tank with water. Literally trickle the water in. I pour the water at a very slow rate into a shallow bowl placed on the substrate. If you pour too quickly and disturb the layers below, laterite (or other amendments) can cloud the water badly for days, and turn the water red for longer than that. It is possible to diatom the mess out of the water, but that just removes the nutrients so carefully added to the tank. I like to be able to enjoy the beauty of my tanks from the first day. It’s not hard to accomplish as long as you take your time.

Malaysian Livebearing Snails

Another “additive” that some people use in the substrate of planted tanks are Malaysian livebearing snails. These are very small, nocturnal burrowing snails. You won’t even see them most of the time if the water quality in your tanks is good. They act like aquatic earthworms, burrowing through the substrate, keeping it from compacting, and eating detritus and leftover food. Unlike many other species of snails, they do not damage plants.

Substrate Maintenance

In a well-planted tank with healthy growth, you won’t need much. Some people who do extremely well with their plants never touch the substrate. Because my tanks are first and foremost display tanks, I try to be a little more middle of the road about it. I do use a gravel vacuum, but I only go over the surface very gently in the areas around the plants in order to pick up loose mulm. I do not try to dig into the gravel in these areas. If a tank has a substantial open area without any plants, vacuum this area as you would in any other tank. You can purchase a small-diameter gravel vac that is particularly useful for removing detritus from the surface of the substrate in densely planted areas, particularly in smaller tanks.

A planted tank is in many ways like a terrestrial garden. The best plants in the world will not thrive if they are not cultivated in appropriate soil. The same is true of their aquatic counterparts. Take the time to meet the needs of your plants and they will give you and your fish pleasure for a long, long time.

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