One of our fellow club members has a problem many of us would like to have. His Amazon swordplants grow too large for his 50-gallon tank and he has to get rid of them periodically! One of his monster plants was on auction last May, and it was very impressive. It was a beautiful melon sword (Echinodorus osiris) with a flowering stalk. He kept some of the plantlets from the stalk and they are growing quite well.
So what’s his secret? It is a combination of many factors, the primary ones being quite basic. His plants get good light and proper fertilization: macro-nutrients, micro-nutrient supplements (mainly iron), and carbon dioxide.
The tank is illuminated by three 20W GE fluorescent plant lights, lit 14 hours per day. The lights sit over the glass cover and are controlled by a timer. The plants are close to the lights and have a regular day and night cycle. The plant lights have a spectrum geared towards healthy growth and yet their colour is close enough to white light that the fish don’t look weird when viewed under them.
The gravel is smooth and on the larger side (over 5 mm). The large-sized gravel looks good, but it has the drawback that uneaten food and fish waste can accumulate in the gaps between the grains. In a fish-only tank, this means lots of vacuuming to keep the substrate from going anaerobic and creating problems. On a planted tank however it can be quite beneficial. All this waste is plant fertilize; the macro-nutrients I mentioned earlier. Amazon sword plants and many other plants with an extensive root growth are heavy feeders. They develop extensive root structures in this substrate, keeping it from going anaerobic and breaking down the fish waste.
Another factor is micro-nutrient fertilization. If you look at the soil in the tropical regions you will notice that it is often reddish in colour. This is caused by the presence of iron and manganese. In some areas there is so much iron that it precipitates as a rusty dust on the bottom of the streams. Our tap water, in comparison, is lacking in iron, so we must add it to our planted tanks. One sure sign of iron deficiency is a glassy, yellowish, look to the plant leaves. Once iron is added, the leaves turn bright green and grow larger. A little goes a long way with micro-nutrients, so make sure you use a commercial preparation for aquarium use, or buy an iron test kit and use iron chelate.
Last but not least is carbon dioxide. During the day the plants use it up when building their cell structure and return dissolved oxygen to the water. The carbon dioxide here is provided by simple yeast fermentation. A four-litre carboy with stopper and tubing leads to an airstone inside the tank. It contains a solution of sugared water and bread yeast, and can provide carbon dioxide for four to six weeks before replenishment.
The whole tank is filtered by an Aquaclear Mini, and is well stocked with fish and plants. Though the filter is undersized for the tank, it provides valuable water movement that circulates nutrients. The lush plant growth contributes greatly to the water quality. This setup requires regular bi-weekly water changes of ¼ of the tank’s volume.
Keep in mind that Liebig’s Minimum Law governs plant growth. That means that the growth factor present at a minimum determines the growth rate. This is called the limiting factor. In this setup the limiting factors are carbon dioxide and iron. Leave out the carbon dioxide and the plants stop growing. Leave out the iron supplements and the leaves become chlorotic (the glassy yellow look). Lights can also become the limiting factor if not changed often enough (fluorescent), or are not bright enough. If you would like to try carbon dioxide fertilization, the yeast recipe is the most inexpensive way. Many experts think it is a waste of time and money on the long term, but if you don’t want to mess with high-pressure cylinders, valves and regulators, it is the safest alternative. Here is the recipe I use, adapted from one in the rec.aquaria FAQ on the Internet:
- Put four cups of sugar in a four-litre carboy.
- Fill with water up to the point where the width starts tapering to the neck. Stir or shake well until it is all dissolved. Be careful not to spill the whole thing.
- Dissolve ¼ of a teaspoon of baker’s yeast in a little bit of warm water. Pour it into the carboy and stir well.
- Put the stopper in the carboy and it should start bubbling almost right away. By the next day the pressure would have built up enough to bubble in the tank. If it hasn’t, look for leaks.
Some people recommend using pop bottles, but I found that it is very hard to get an airtight seal in them once one drills a hole in the cap for the air tubing. Silicone does not stick well to plastic, and any little leak usually means no bubbling in the tank. The carboy and stopper work much better.
Before experimenting with carbon dioxide fertilization, make sure your tank is well-planted and under-stocked. Even in a 50-gallon tank, the above setup can cause sudden shifts in pH when the carbon dioxide is first started or suddenly stopped. This can be stressful to the fish. Also, insufficient light or insufficient plants may result in higher than ideal carbon dioxide concentrations in the water, again stressing the fish. Therefore I recommend that such fertilization be done after the tank has had time to settle, and it is running well. Then you can watch your plants grow without worries.?