Theory Thursdays: Managing Plants in the Freshwater Tank

Two weeks ago today, I put up a post about chemistry tests for fish tanks, and I kept mentioning various compounds as being useful for aquarium plants, and then habitually refused to say more about it, citing that I would explain plant chemistry in a bit more detail later.

Well, here I am! And I'm ready to talk about it all.


First of all, it's important to note that plants are like fish - there's no such thing as the "right water conditions" for plants in general - different plants like different water conditions. The best way to figure out what you need for your plants is to look them up in a database like that hosted at http://plantedtank.net. The easiest way to do that, of course, is to take the species name and look it up directly - if I'm doing my job properly I can usually get that done for you on your slip so that you can look them up when you get home.

For an example, let's consider a common plant, Amazon Sword, which you can see plenty of in the above photo. The species name is Echinodorus amazonicus, and when we look it up we find it is native to Brazil. We also find some very useful information, like the water temperature it likes, the speed at which it grows (and, therefore, the demand it places on your fertilization setup) the pH needed, the lighting, and so forth.

Well, what does all this mean? For starters, you're going to want to stick to plants that like the same pH and temperature range as each other and any fish you might happen to have in your tank (at the moment, I have some plants all by their lonesome in a little 5 gallon).

You'll also want to do a mixture of fast and slow-growing plants. Slow-growing plants provide cover and visual appeal, where fast-growing plants, usually grasses of some sort, are mostly useful as a form of nitrogen sink - they consume nitrates. The more fast-growing plants you have at your disposal, the better you can do in terms of controlling nitrates. This will never eliminate the need for frequent partial water changes, but the reduced "ambient" Nitrate levels will also help curtail algae growth.

In general, the best way to maintain a healthy chemistry level is to use a product like Nutrafin Plant Gro as directed - in heavily-planted setups, it may be necessary to deviate. You also don't need CO2 injection, no matter what anyone tells you, unless you either have a really low bioload or you are aggressively growing plants under very high lighting conditions - see the Dutch Tank concept.

As for lighting, the easiest way to determine how much you have is to divide the wattage of the bulb you are using by the number of gallons in the tank. My 55 gallon tank has 108 W of light over it, for about 2 L per gallon, which is medium illumination. At this light level, I can reasonably expect plant die-back in medium and low light plants to halt. Colour temperature and bandwidth are also important - ask at your local pet store for the right kind of bulb or seek out Hagen Life Glo, Power Glo, or Plant Glo elsewhere.

Of course, these rules almost all vary plant-for-plant, but if you read up on the individual plant species, you'll have far better luck for plant care than any rule of thumb I could give you would.