Geting Started With CO2

Caron dioxide (CO2) systems have been available for planted aquariums for quite some time. Like many people, I thought that they were rather complicated, high-end systems that were also expensive to purchase. I’ve discovered over the past year that they are affordable, easy to operate and very beneficial to live planted aquariums.

I have to say that, despite keeping fish for about 17 years, I’ve been firmly in the plastic plant camp for most of that period. I have set up live-planted tanks in the past. In fact, I won the Agriculture Exhibition’s Best Adult Freshwater Aquarium trophy three times in the days when only live plants were allowed. However, those tanks tended to be set up specifically for the competition and were never maintained long-term. My focus has been primarily on keeping cichlids, which don’t always co-exist with live plants. As a result, I’ve tended to concentrate on the fish and used plastic plants for decoration. However, I have always found live-planted tanks to be very attractive.

Some years ago, I purchased the book “The Optimum Aquarium” by Horst and Kipper. The book is an excellent resource for those considering planted tanks but the methods proposed by the book do tend to be rather intensive, promoting CO2 injection, under-gravel heating cables, special substrate and metal halide lighting. I was tempted to try it but it still seemed like too much trouble and too expensive. The book stayed on my bookshelf and I stuck with cichlids and plastic plants.

About a year ago, I decided that I would finally try installing a CO2 system on the 75-gallon tank in my kitchen. The tank housed a group of wild red-spotted Peruvian Angelfish and a pair of Mesonauta insignis that I brought back from a collecting trip to Peru. There were also some other inhabitants in the tank. I had recently acquired some plants from Jeffrey Porter and decided that it was time to try a CO2 system.

Before moving on to talk about the system that I bought, I should probably give a basic explanation of what CO2 does, and why it is beneficial to aquatic plants. Putting it simply, plants grow through a process called photosynthesis that requires light and CO2. During daylight hours, plants absorb CO2. During darkness, plants release oxygen. Increased levels of light and CO2 can result in better growth rates in plants. Remember that this is a very simple explanation and further reading would provide a more in depth explanation of the entire process.

After doing a little research it became apparent that I had three basic choices to make concerning the level of automation in the system. I could go with a basic system that continued to dispense CO2 at the same rate around the clock. The problem with such a basic system is that plants do not absorb CO2 when it is dark. CO2 also lowers the pH in the tank. Therefore, during the hours of darkness the excess CO2 can drastically reduce the pH in the tank until the lights come on and the plants begin feeding again. The resultant pH swing can be detrimental to fish in the tank. The second and third options are designed to avoid injecting CO2 into the tank during the hours of darkness, thereby avoiding this problem. A fully automated system employs an electronic pH monitor. When the pH rises above your pre-set level, the CO2 system kicks in and injects CO2 until the desired pH level is reached, and then switches off again. Whilst this ‘bells and whistles’ fully automated system might seem like the best way to go, I have had experience with electronic pH monitors in the past. In my experience, they need to be regularly calibrated in order to be reliable and I didn’t really want to go through monthly calibrations. The other option is the ‘semi automatic’ system that involves plugging the system’s electronic solenoid into the same timer that controls the tank’s lights. This ensures that when the lights are on the CO2 is injected into the tank but when the timer switches off the lights, the CO2 is turned off also. After considering the options, I decided to go with the ‘semi automatic’ system.

Having decided on the semi-automatic system, I then had to decide on how the CO2 would actually be dissipated into the aquarium. I found information on a couple of reactors that are placed inside the aquarium but they didn’t appeal to me. If I am trying to create a nice planted display, I don’t really want a piece of plastic in there that I then have to hide somehow. During some web surfing, I came across the Aqua Botanic site. They were selling a reactor that is fitted inline with a canister filter (outside the tank) so that the CO2 is mixed into the water as it leaves the filter and before it is pumped back into the aquarium. I decided to go that route and purchased my system from Aqua Botanic. I should point out that Aqua Botanic no longer sell this reactor but plans are available online for a similar home-made reactor.

The system that I purchased consisted of a CO2 regulator with an electronic solenoid and built-in bubble counter together with the CO2 reactor. The US price of the regulator was $99.95 and the reactor was $31.99. Of course, shipping and import duty added to the cost. I subsequently purchased a 5lb CO2 cylinder from Barritt’s but soon discovered that whilst its small size allowed it to be stored out of sight under the tank, it would only run a 75-gallon tank for 3-4 weeks. By contrast, a rented 20lb tank runs for about 3 months. Also, when using the rented tanks, you can drop off the empty and take a full tank without waiting. When using your own smaller cylinder, you have to leave it at the facility for refilling and return to collect it later – often the next day. Anyway, let’s get back to setting up the system.

The inline CO2 reactor is a home-made contraption that consists of a piece of PVC pipe with end caps, filled with small pieces of lava rock. The online plans for a similar system uses plastic bio balls instead of lava rock. There are barbed fittings on each end-cap to accept flexible rubber tubing and there is an air valve towards one end of the pipe for the CO2 inlet tube. To keep the reactor vertical, I zip-tied it to a wooden kitchen towel holder. Nothing fancy but it does the job. I then fitted the outlet pipe from the canister filter to the top of the reactor. A pipe from the bottom of the reactor takes the water back to the tank. The idea is that CO2 is pumped into the reactor and begins to rise vertically through the lava rock. At the same time, the water is being pumped downwards through the reactor. The CO2 is absorbed by the water whilst in the reactor and is pumped into the aquarium.

With the regulator attached to the CO2 cylinder, the gas is only pumped into the reactor when there is electricity going to the electronic solenoid valve (when the light timer is ‘on’). The CO2 then bubbles up through the bubble counter, along some tubing and into the reactor. A knob on the bubble counter allows a fine control of flow rate of the bubbles.

Initially, the system was set up with a flow rate of about one bubble per second. After a couple of days of operation, I began to test the water in the aquarium so that I could properly adjust the flow rate. I found a very useful chart online at George Booth’s Plant FAQ (see references) that allows the CO2 level to be determined by measuring pH and KH hardness. After a couple of days of adjusting and re-testing, I found a setting that kept my pH at about 6.8. I had constant KH hardness readings of 3 degrees (53.7ppm) so with a pH of 6.8 the calculated CO2 level was 14 milligrammes per litre (mg/l). With a pH of 6.6, the CO2 level increased to 22 mg/l. It is my understanding that plants do best at about 15 mg/l so maintaining a pH of 6.8 with a KH hardness of 3.0 seems about right.

I can attest to the fact that, once set-up, this system doesn’t require a lot of tinkering. I set up my system in December 2004. By early February I was satisfied with the settings and hadn’t tested the water since. Now, in October 2005, I have tested the water again for the purpose of this article. I found that the pH was 6.4 and the KH hardness was 3 degrees, giving a calculated CO2 reading of 35 mg/l. After 8 months of basically being left alone (except for changing over the CO2 cylinder every 3 months), the system was still operating within acceptable parameters. This latest test may mean that I need to adjust the bubble counter slightly but the test was conducted when the tank was in need of a water change, which may have affected the pH readings. The point stands, however, that these systems can be set up and allowed to do their thing. They do not need constant attention and calibration.

I mentioned earlier that, in addition to CO2, plants need light to grow. My aquarium has two basic four-foot light strips that each hold two 24 inch fluorescent tubes. I have two Zoo Med Flora Sun (plant growth) tubes at the rear and two Zoo Med Ultra Sun (Super Daylight) tubes at the front. The timers are set to give ten hours of light from each, but they are slightly staggered so that they don’t both come on and go off at the same time. I have never bothered to measure or calculate lux levels from this lighting system. Remember that I’m trying to keep it fairly simple!

In addition to light and CO2, plant fertilizer supplements are often recommended. There are so many products available on the market but I chose to go with three additives, all made by SeaChem. I use SeaChem’s Flourish, Flourish Trace and Flourish Iron. I add doses of each of these once per week. There are a number of other supplements in the SeaChem line but I have stuck with these three. My maintenance programme is basic – a 40% water change every two weeks. Filtration is provided by an Eheim canister filter.

So, does this work or is it snake oil? It absolutely works! Within a month of setting up the system, I could see a noticeable improvement in the growth of my plants. In the past ten months of operation, I have been very pleased with the plant growth. Notoriously slow-growing Anubias plants are regularly putting out new leaves and have even flowered. My Anubius frazeri plants have grown particularly well and are now quite tall. I recently purchased some more A. frazeri at a club auction. Those specimens had been purchased from Jeffrey in late 2004. They looked as though they had hardly grown since being purchased and were puny in comparison to those in my tank. Since being placed into my tank, those same puny plants have doubled in size and are now growing well. Of course, one of the major challenges is the limited availability of aquatic plants in Bermuda, so we have to make do with the limited species that are available. However, despite the lack of variety, I have been able to establish a live-planted tank that I am happy with.

After ten months of operation, I am very pleased with the choices that I made when purchasing my CO2 system. I like the semi-automatic method and I have no intention of ‘upgrading’ to a fully automated system – this works just fine for me. I also like the reactor that is out of sight in the tank stand. The only mistake that I made was purchasing the smaller CO2 cylinder. The 5lb cylinder would be great for someone running a smaller planted tank but it doesn’t last long enough for a 75-gallon. I hope that I’ve been able to remove some of the mystery surrounding CO2 systems and demonstrate that they are easy to operate and not particularly expensive.

References:
Aqua Botanic Store - http://www.aquabotanic.com/abstore/index.html
Aquaticscape (undated) ‘External Inline CO2 Reactor’, http://www.aquaticscape.com/articles/co2reactor.htm (accessed 5th October 2005).
Booth, G. (1995) ‘George Booth’s Plant FAQ’, http://hallman.org/plant/booth1.html, (accessed 20th December 2004).
Horst, K. & Kipper, H. E. (1986) The Optimum Aquarium, West Germany, AD Aquadocumenta Verlag