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The 10 Gallon Plant Tank

Dan Resler

The mail arrives with the latest issue of Aquarium Fish Magazine. You eagerly snatch it up and turn to the table of contents. You note and then quickly turn to the article on plant tanks. And then the discontentment sets in.

For as you scan the beautiful pictures accompanying the article your pride-and-joy 10 gallon tank in the corner just doesn't look as good as it used to. Sure, you've got a clump or two of plants that look quite nice now, but you know that it'll only be a matter of weeks before they turn brown and mushy and you'll have to replace them yet again.

So you open the dog-earred mail order catalog and do some calculations on what it would cost to duplicate the set-up you see pictured in the magazine. And you quickly come to the same conclusion you've reached many times before---there's no way you can afford it.

But this time you're wrong!

In this article I'm going to present a very simple way for you to have a flourishing, beautiful plant tank for a tiny fraction of the cost of the high-tech tanks featured in various books and magazines. And for the most part you'll be able to use the equipment you already own. All you will need to do is make a few changes in your lighting, water chemistry, and substrate.

One more comment before beginning; the suggestions that follow are made assuming that the reader is already properly maintaining their tank through weekly partial water changes and periodic filter and tank cleaning, and that their tank is not overstocked or housing fish that are generally incompatible with plants (like substrate diggers, for example).

Full-Spectrum Lighting

Probably the first area you'll need to tend to is the type of lighting you're providing for your tank. There are two important factors to consider when providing a light source for plants---the light's spectrum and its intensity.

Although aquatic plants tend to be remarkably forgiving when it comes to the type of light they can utilize, they will do best under so-called full-spectrum lighting. `White' sunlight is actually a mixture of many colors; anyone who has ever used a prism has seen a demonstration of this. It has been show that plant photosynthesis `prefers' certain colors in the spectrum over others; ideally the artificial light for our tanks would be composed of light in these colors. Many of the full-spectrum fluorescent bulbs on the market today were designed to do just that.

Unfortunately most of the 10 gallon tank strip lights restrict you to using a single 15 watt fluorescent bulb. This is not much light, and since all 15 watt full-spectrum bulbs are not created equal, it's important to try to select the most intense full-spectrum bulb available. While I've yet to see a comprehensive and objective study comparing the intensity of these bulbs, there is some evidence that the so-called `triphosphor' bulbs are the most intense. Two examples of such bulbs are Aquarium Product's Triton and Penn-Plax's Ultra Tri-Lux. I have used a single 15 watt Triton bulb with great success in my 10 gallon plant tank.

The photoperiod or amount of time you should leave your lights on is worth mention as well. A photoperiod of 10--12 hours is considered the best for plant tanks; use a timer to control consistency. It is also important to realize that having the lights on longer is not a substitute for poor intensity---you should not cut corners on getting an intense, full-spectrum light source.

One thing else; try to avoid placing your tank near a window where it would receive direct or strong indirect sunlight. Although at first this seems counter-intuitive, such a tank would almost certainly receive too much light resulting in a big algae problem. It is better to place your tank in a darker location where you can fully control the amount of full-spectrum lighting it receives year-round.

CO2 Injection

The single most important thing you can add to dramatically increase plant growth in an aquarium is CO2 injection. While many hobbyists are aware of this, the high cost of commercial CO2 systems makes it an impossible option for those with limited resources. However, if one is willing to sacrifice a little control and time, an inexpensive alternative is available.

What do you get after a time if you throw together some water, yeast, and sugar in a sterile jar? Alcohol, of course, in a process called fermentation. But that's not the only product of such a concoction, for a fairly large quantity of carbon dioxide gas is also produced. Redirecting the output from a fermentation jar into your tank will substantially increase the amount of CO2 in solution.

Making such a jar is quite simple and inexpensive. An old plastic soft-drink bottle is an ideal container. Drill a small hole in the cap of such a bottle (or use a one-hole rubber or cork stopper if you prefer) and push through a 2'' piece of rigid tubing. Seal this with silicone aquarium sealer (if using the cap), and attach one end of an airline after the sealant dries. The other end of the airline should be anchored in your tank. (I use an airstone to make finer bubbles but it really isn't necessary.)

Now fill the bottle about 3/4 full with warm (body-temperature) water. (You might want to `sterilize' it first; I completely fill my bottles with water and a teaspoon or so of bleach and let them sit over night, but this is probably overkill. If you do this, be sure to thoroughly rinse it afterwards.) Add approximately 3/4 cup sugar and a teaspoon of baker's yeast, shake vigorously, and then connect the airline. In just a few hours you should begin to see froth on the surface of the jar accompanied by CO2 bubbles in your tank.

I find that CO2 will continue to bubble into the tank for 10-14 days; others have reported longer times. The bubbling is usually much more vigorous at first. Modifying the amount of sugar and yeast will alter the rate the gas is produced as well as the duration. With experimentation and observation it's possible to get a fairly consistent bubbling rate. I try to start a second bottle before the bubbling rate on the first bottle drops below a certain threshold in order to maintain consistency during bottle changes.

While this method of CO2 injection is easy and cheap, there are some drawbacks. Injecting CO2 into your tank lowers the pH, and since this method offers very little control over the bubbling rate, you have very little control over pH swings in your tank. With patience and attention these swings can be minimized, but it's very important that you closely monitor your tank's pH to ensure it remains in a `safe' zone---I would not let it drop below 6. People with very soft water (i.e. with carbonate hardness (often referred to as `alkalinity') below 2 KH) should probably not even attempt this method as it would be very difficult to maintain a stable pH near neutral. (A thorough discussion of the relationship between total and carbonate hardness and pH is beyond the scope of this article; consult the water chemistry section of a quality aquarium reference book for more information).

If a very stable pH is important to you and to the health of your fish, you might want to use the yeast method of providing CO2 just during the break-in of your tank (i.e. before you add pH sensitive fish). More on this later.

For more information about the yeast method of CO2 injection, check out Thomas Narten's article titled DIY CO2 Injection: The Yeast Method in the May-June 1994 edition of The Aquatic Gardener (The Aquatic Gardener is a publication of The Aquatic Gardeners Association; for information, write Dorothy Reimer, 83 Cathcart St., London, Ontario N6C 3L9, Canada).

Laterite, the Substrate, and Plant Nutrients

A newly set-up tank is a pretty unfriendly place for plants. Not only is the standard gravel substrate not an ideal rooting medium for many plants, it is initially devoid of any nutrients that the plants need for survival. There are at least three simple and inexpensive things you can do to greatly improve the chances of your plants surviving their new home.

First, choose a gravel approximately 1/16" (2-3 mm) in size and lay it down to a depth of at least 2.5'' (6.5 cm). Gravel of this size will allow for easy water flow through the substrate while at the same time resisting becoming clogged over time. Your substrate must also be deep enough to allow for unrestrained root growth.

Second, add laterite to the bottom 1/3 of your substrate. Laterite is a red clay-like substance rich in iron that has been show to be of great benefit to plants (see the February 1994 issue of Aquarium Fish Magazine for a more thorough discussion of the benefits of laterite). Although you might have great success without the addition of laterite, I believe your plants will show more vigorous growth initially and prosper longer if a laterite-rich substrate is provided. If you have an established tank and don't relish the idea of having to remove your substrate to add laterite, all is not lost. Laterite can be purchased in the form of 1/2" diameter `balls' that can be gently pushed into the gravel near the base of your plants. (If you can't find laterite at your local pet shop, you might try getting it mail-order from Pet Warehouse (Xenia, OH) or DALECO (Ft. Wayne, IN). Ask for `DuplaRit K' (loose laterite) or `DuplaRit G' (ball form).)

Finally, you should feed your plants. Most tap water does not contain adequate nutrients for aquatic plants, so in the first weeks after planting it is wise to add fertilizer to your tank to eliminate possible restrictions to plant growth. Unfortunately, many so-called aquatic plant fertilizers being sold today are worse than worthless---they can do considerable damage to your tank by encouraging rapid growth of algae or, worse yet, by actually poisoning your fish.

Getting plant tank supplements right is a tricky business; I do not pretend to have the final answers on this topic. I and others have had considerable success, however, in using the Dupla regimen for feeding aquatic plants. Dupla's plan involves both daily drops and supplements added only at water changes.

What about undergravel filters?

``OK'', you're now thinking, ``maybe the old 10 gallon has some potential after all. But what about my undergravel filter? I've heard you can't grow plants in tanks with undergravel filters.''

This view, I'm happy to report, is nonsense. It may be more difficult raising plants with an undergravel filter, but it is by no means impossible. Many people have successfully set-up and maintained beautiful plant tanks of all sizes using undergravel filters.

An undergravel filter does, however, make it more difficult to use laterite in the lower portion of your substrate; much of it would probably end up suspended in your tank due to the relatively high flow of water through the gravel. This problem can be minimized by using the before-mentioned laterite balls near the roots of your plants instead of mixing `loose' laterite into the substrate.

Another potential problem with using an undergravel filter is the common practice of using air bubbles to draw the water through the filter. Injecting CO2 will cause the CO2 concentration in your tank to be considerably higher than it is in the surrounding air. This excess in your tank will naturally escape into the atmosphere over time, and aeration or excess agitation of the water surface will increase the rate at which this happens. The result will be a lowering of the CO2 concentration in your aquarium. All aeration should therefore be removed from your tank; instead, use a low-power power head for your undergravel filter.

Planting and Tank Break-in

The first few weeks after planting are crucial to the success of your new plant tank. In most plant tanks there is a battle for dominance between the higher-order plants and algae. It is important during this time that your plants out-compete the algae for nutrients and win this battle. Two things are desirable during this time---rapid plant growth and algae eating fish.

The CO2 injection, full-spectrum lighting and fertilizer supplements will produce the needed rapid plant growth, providing you plant fast growing plants. Some examples of good fast-growers to start with are Hygrophila polysperma, Cabomba caroliniana, Bacopa caroliniana, Egeria densa, and most Aponogetons. Amazon Swords (Echinodorus bleheri) also do well but I have find that they quickly get too large in a CO2 injected 10 gallon tank. Stay away from floating plants at first as they will tend to block out too much of the light needed by other plants. Also be sure that your initial planting is dense---assuming `normal' distances between plants, you should aim to cover at least 75% of your substrate.

To help keep the algae in check, I recommend adding at least two Black Mollies to your tank. Black Mollies can be excellent `nibblers' of algae providing that is their only food source. In other words, it is very important that once you introduce the Mollies to your new plant tank that you do not feed them for 2 or 3 weeks. They will survive (providing they were healthy to begin with) and will greedily attack any algae that dares to show up during this time.

This of course poses a problem if you're modifying a tank that's already set-up and populated with fish. If this is the case you might want to introduce the Mollies but restrict feeding to every 3rd or 4th day. This should still encourage them to eat some of the algae while also providing enough food to keep the tank's other occupants alive.

Dealing with the Jungle

A 10 gallon tank does not provide much room for plants to grow; if all goes well during the break-in period (approximately the first 6 weeks), you're going to find that your plants are quickly outgrowing their new home.

One solution is diligent pruning. Many of the so-called `bunch' plants will do better, however, if they're trimmed from the bottom. Pull the plant out of the substrate, lop off the bottom portion, and then replant. Roots seem to be easier to grow than new stems and leaves. Other plants, such as Amazon Swords and Aponogetons, cannot be trimmed in this manner, but you can usually just remove those leaves that have gotten too large. Vallisneria can be snipped off at the top without damaging the plant.

Don't be afraid to rearrange the plants as they grow; rarely is an initial planting satisfactory after a few weeks of growth. Simply pull up the plants you want to move and replant them in the preferred place. Most will recover quickly in a CO2 injected tank.

A second solution to dealing with a `jungle' is the one I prefer for a 10 gallon tank. After the break-in and when you're finally happy with the plant assortment and aquascaping, and your plants are growing like crazy, discontinue the CO2 injection. Not only will this greatly slow down plant growth but it will also allow the pH to stabilize. With adequate light and nutrients your plants should continue to do well.

What about my 20 gallon tank?

The modifications suggested in this article `scale-up' quite nicely; in fact, it is generally easier to set-up and maintain larger plant tanks. A larger volume of water is more stable plus your plants have more room to grow before they need pruning. Aquascaping can also be easier if you have more area to work with.

The yeast method of generating and injecting CO2 will also work well with larger tanks. Most of the CO2 that bubbles into the 10 gallon tank is `wasted'---it harmlessly escapes into the atmosphere. Therefore with larger tanks it is usually not necessary to generate more CO2 but instead to somehow provide a means where more CO2 can get into solution. One simple way to do this is to trap the gas by bubbling it into an inverted bowl where it will remain in contact with the water for a longer time, therefore allowing more to go into solution. Remember to monitor your pH very carefully to make sure it doesn't drop to dangerous levels.

Another concern with larger tanks is light intensity. Deeper tanks require substantially brighter lights to provide adequate illumination at the substrate level. You should strive to provide a minimum of 1.5 watts per gallon (using the advertised tank volume, not the actual volume) of intense full-spectrum lighting for tanks up to 24'' deep. And closer to 2.0 watts (or more) per gallon would be noticeably better. Fortunately this is not difficult to do as there are a variety of dual and quad light strips and hoods on the market today for larger tanks.

With a little care, ingenuity, and patience it is possible to create beautiful plant tanks on a limited budget. Hopefully I've given you a few ideas to get you started; don't be afraid to experiment and try out new ideas. Keep learning, and enjoy!

Dan Resler
Dr. Resler is a professor of Computer Science at Virginia Commonwealth University.
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This page was last updated 19 September 2000