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Benefits of Carbon Dioxide

The addition of carbon dioxide in a planted aquarium will make a big difference in plant growth.

By Karen Randall

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Q. I've kept a well-lit, low fishload, heavily planted 65-gallon aquarium for almost a year — low tech and low maintenance. My plants and fish are doing well. I use trial and error with plant species and positions, and fertilizing regularly with Seachem's "Flourish" (liquid and solid). I'd managed to avoid the lure of CO2 injection, primarily because of my own laziness and fear of change, but one of your articles changed that. The diagram and description of the homemade CO2 system made it seem so simple I decided to try it.

Within 10 days an Aponogeton ulvaceus was sending up a 3-inch flower stalk. I'm writing to you four days later and the stalk is now 24 inches and floating on the surface of the water with a big bud! Not only that, but tonight I noticed both Aponogeton crispus (my favorite) and Echinodorus amazonicus have produced flower stalks too!

So, do you think it's the CO2 or the rapid change in pH from 7.0 to 6.6 that made the difference? Do you think my Aponogeton madagascariensis will bloom, too? Would it be better to let the plants put energy into root/leaf production by removing the buds?

A few years ago I knew nothing about fishkeeping, not to mention underwater gardening. But thanks to a few good books, excellent magazines like Aquarium Fish international magazine and a great local fish store, I have a little miracle happening in my living room.

A. I have seen plants, even if they were growing moderately well before the addition of supplemental carbon dioxide (CO2), suddenly bloom when CO2 is added. Because some plants will bloom in response to environmental changes, I hesitate to say that the bloom was brought about specifically because CO2 was added. That said, it is amazing what CO2 supplementation can do for an aquarium that is otherwise well supplied with nutrients and light. The amount of new growth and the health of that growth can improve dramatically with the addition of even small amounts of supplemental CO2.

Aponogeton, in general, is one of the easiest genera to bloom in the aquarium. And, yes, even your Madagascar lace plant may very well bloom too. Unfortunately, blooming does not always equate with vibrant health in Aponogeton. Aponogeton often bloom as a precursor to entering their dormant phase, although they can also bloom without going dormant afterward. Removing the bloom will not prevent the plant from entering dormancy, so enjoy it!

The thing that makes Aponogeton so "foolproof" in the beginning is that they are living off the nutrition stored in their tuber. Therefore, even in the poorest conditions you can get a good show out of them, at least for a few months. In the average aquarium dedicated to fish — typically deficient in light and nutrients — the plants eventually deplete their internal nutrient reserves. Because they were unable to store an adequate new supply of nutrients during their growth phase, they are unable to break dormancy and return to their former beauty.

In an aquarium that is well supplied with a nutritious substrate, plenty of light and supplemental CO2, Aponogeton can often store enough nutrients that they can be brought back to their former beauty after their dormant period. It certainly doesn't hurt to try to bring an Aponogeton through dormancy, but keep the above in mind, and don't be disappointed if it doesn't work. My preferred way to rest Aponogeton is as described below.

Once the leaves have died back, remove the tuber from the aquarium and place it in a small container of damp sand or fine gravel. It does not need to be submerged in water. Seal the container and place it in a cool dark location, like a corner of the basement. I have found that the refrigerator is too cold for most species. After six to eight weeks, the tuber can be returned to the aquarium, where, if all goes well, it should sprout and begin to grow within a couple of weeks.

One nice thing is that in recent years aquarium plant growers have produced a number of Aponogeton hybrids that can grow in the aquarium for extended periods of time without going dormant. Some plants can go for years without entering a dormant phase.

I'd like to comment on your "great local fish store" too. These gems are few and far between, and unfortunately, in these days of mass merchandising, can easily be driven out of business by the big chains.

Readers, if you have a great local fish store, support it in any way you can. Buy your supplies from them even if they are a few pennies more than mail order. Suggest that other hobbyists frequent this store. And don't forget to tell them how much you appreciate their help!

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