The CO2 Calcium Reactor.
In the third part of my series on methods of maintaining levels of calcium and carbonates in the reef aquarium I’m going to take a look at CO2 calcium reactors. These are, perhaps, the most expensive pieces of equipment commonly purchased to maintain calcium and carbonates, but they can be the cheapest to run. Why is this such an expensive route to take? Well, when you first go this route, you find you actually need to buy two items of equipment, not just one, which of course pushes the price up. For a calcium reactor to work you also have to buy a CO2 bottle plus control gear at the same time as buying the actual reactor.
How does it work?
A CO2 reactor is a container used to hold calcareous media through which tank water, mixed with CO2 gas, is passed. By adding CO2 gas to the tank water, the pH value of the water is reduced, when the pH drops into the range of 6 to 6.5 pH it’s then acidic enough to dissolve the calcareous media, The water that leaves the reactor is high in calcium and carbonates which are now available for corals to use in the process of calcification – skeleton building. What’s more, the calcium and carbonates made available by this method are in the correct balance that’s so important for the reef aquarium.
How do you set up a CO2 calcium reactor?
It’s common practise to run a calcium reactor of this type by either tee-ing off from existing pipe work or by using a small, dedicated pump for the purpose. The flow of water through one of these reactors is generally quite low, as you’ll see when I describe how they are controlled.
With this type of reactor you can control the output by both adjusting the rate at which CO2 is fed to the reactor and by regulating the flow of water through the reactor.
To help control the rate at which the gas is fed into the reactor a device called a bubble counter is employed. This is simplicity itself, a small transparent container that is part filled with water and positioned so that the gas flows through it on the way into the reactor. You can then observe bubbles of gas moving through the water and, as the name suggests you count the bubbles as a way of quantifying the delivery.
The amount of water passing through the reactor is controlled by restricting the flow before it reaches the reactor and, again, this flow is quantified by observation, only this time you measure the flow by counting the drops of water returning to the aquarium over a given period of time. So, at the simplest level, you can control the reactor by a combination of bubbles of CO2 per second and drops of water per second.
Now, just because this is such a simple method it certainly doesn’t mean that it’s an inferior one; in fact, although it may seem a bit basic, it has the virtue of simplicity. You can see at a glance that water and gas are feeding through the system, and a quick bit of mental arithmetic will confirm that the flow rates are correct. Compare that to the more high-tech approach, where it’s impossible to tell just by looking if a pH probe is running accurately, or if an electrically operated solenoid valve is open or closed.
The production of the reactor can be evaluated simply by testing the water being fed back to the tank. Measure the alkalinity (in this case the quantity of bicarbonates and carbonates not a measure of acidity) of this water; the value here will be most usually be read in either meq/l or dKH (1.0 meq/l = 2.8 dKH), the higher the reading, the higher the reactor’s output. Although this can be useful, remember it’s the levels of calcium and carbonates in the aquarium that really matter.
A more technical solution to controlling the output of this type of reactor is to add a probe to measure the pH level within the reactor, a solenoid to turn the flow of CO2 on and off, and a controller that can be set to operate the solenoid at a given level of pH. As the way this reactor operates is by acidifying the water we can use the resulting pH reading as a guide to the correct operating of the reactor. Generally we’d be looking at a pH of somewhere in the region of 6.0 to 6.5, although the optimum level will be dependent upon the media being used in the reactor. Different types and grades of media will differ in the ph required to bring about the release of calcium and carbonates, and ideally we would like to use the media that works for us at the highest pH level we can manage. The reason for this? Well, one of the downsides of this type of calcium reactor is that lowering of the tank’s pH can occur.
Note: in addition to type and grade of media influencing the pH level required to operate the reactor, poor quality media can also release phosphate into your reef system. I recommend checking the amount of phosphate your chosen media releases by using an appropriate test kit.
Correcting low pH.
The water returned to the tank is high in calcium and carbonates, but has a low pH in the range of 6.0 to 6.5. Over time this will tend to depress the overall tank pH. To a certain extent, a lower pH isn’t much of a problem, as corals will still calcify down to 7.8 pH. But what may happen is that the lower pH will be responsible for helping to fuel outbreaks of undesirable algal growth.
There are a number of ways of dealing with this lowering of pH. A reef with high levels of surface agitation or excellent gas exchange may experience no problems whatsoever. So, one of the simplest methods is to just use increase gas exchange within the aquarium – this will gas off excess CO2, enabling a more natural pH to be maintained, say around 8.2. This can be done by increasing flow in the tank, or by increasing the rate water is returned to the sump. Simply adding an air pump to aerate water in the sump can also be an effective measure.
A more advanced method is to add a second reactor chamber containing more calcareous media, the theory here is that the acidic water will release more calcium and carbonates from this extra media, and that this, in turn, will use up the excess acidity. This reactor can also contain phosphate remover to negate any phosphate released from the media.
By running kalkwasser in conjunction with a CO2 reactor, you can take advantage of its high alkalinity to counterbalance the acidity produced through the use of CO2.
There are a few potential dangers inherent to the CO2 reactor. Some of these are dangers to the aquarist and his family; others are to the reef tank.
The CO2 bottle containing the gas is pressurised to 50 bar or 725 pounds per square inch (PSI). This is a potential bomb or, more accurately, rocket. The greatest danger lies at the point where the valve or regulator attaches to the bottle – if the bottle falls over, damaging this region or possibly breaking off the regulator, the sudden escape of gas under pressure can propel the gas bottle in the same way as a rocket engine. This is a reaction that won’t stop until the gas is exhausted. A pressurized gas cylinder can, with the valve broken off, become a rocket attaining a speed of thirty-five miles per hour in around a tenth of a second. So, the number one tip here is to restrain the bottle to prevent it from being able to move. In the case of smaller bottles, many manufacturers supply simple brackets that hold the bottle securely in place. For larger bottles you may need to secure the bottle to a wall, or the side of your cabinet, with a chain of the sort used in industry.
CO2 bottles should be stored upright and away from heat. If a bottle overheats, the gas pressure within the bottle can rise to a point where the safety valve will release the contents of the bottle to the atmosphere. This can be both distressing and dangerous, particularly in an enclosed space, for example while transporting a gas bottle in your car on a hot day.
The danger to your reef is that if your system is incorrectly set-up or if “little fingers” start fiddling with the settings, it’s quite possible to depress the pH level of your reef to dangerous levels. So, firstly ensure that you set your reactor up properly, and that when first setting it up, you check and recheck the performance of your new acquisition until you’re happy that it is set correctly. As far as outside interference goes, well, there’s education, or perhaps more reliably, placing the bottle in a location where the settings can’t be changed by a third party. Some manufacturers have safety measures of one sort of another to prevent inadvertent or casual adjustments.
If your control mechanisms fail, you could end up with the entire contents of your gas cylinder being dumped into your aquarium, resulting in a devastating lowering of pH with the potential to wipe out your system.
Pros and cons.
- Initial expense.
- Tendency to lower the pH of the system.
- The possibility of phosphate being released from the calcareous media.
- Once you’ve got over the initial cost of this system you’ll find it very economical to run.
- For larger tanks, and ones with a high demand owing to a high population of stony corals, this can be the only economical of supplying the necessary amount of calcium and carbonates.
- Once set up, apart from a daily glance at the bubble counter and the drip rate, there’s nothing else to do except enjoy watching your corals grow.
- Gas or media replacement is only needed infrequently, giving you more time to spend on other tasks.
- Apart from carrying out a bit of appropriate equipment maintenance when you replace the media or gas bottle, this method requires very little input on behalf of the aquarist.
(I think that by this point you’ll have got the message that, if set up correctly, it’s a doddle, requiring little or no attention except for keeping an eye on bubble rate and drip rate. All in all a very low maintenance, non- time consuming method of keeping calcium and carbonates at the correct levels and balance.)
Hints ‘n’ Tips.
- When you’re preparing to fit a new or refilled bottle, it’s worth “cracking” the bottle. This term refers to the practice of opening the valve of the bottle a little way, then closing it again prior to fitting the regulator. This results in a loud crack, and the resultant displacement of any muck from the valve that might other wise block up the regulator, preventing the flow of gas.
- When the gas in your bottle is nearly used up you’ll find it becomes empty very quickly. Don’t get caught out.
- As most CO2 kits come with a small capacity bottle, I’d recommend purchasing a more realistically sized bottle, say one of two litre capacity. When the larger bottle is exhausted, use the small bottle to run your tank while you wait for the empty bottle to be refilled.
- If using an air pump to help bubble off excess CO2, try using a rigid pipe in place of an air stone.
- Don’t be tempted to cut costs by using cheaper calcareous media. Poor quality media may have the unwanted side effect of releasing phosphates into your reef.
- If phosphates are released from the media this can be easily remedied by dripping the product water into the aquarium through a quality phosphate remover such as that produced by Reef Scientific.
The three different ways of maintaining calcium and carbonates that I’ve covered in this series all have their own pros and cons:
If you have a small reef, then you can’t really go wrong using a Balanced Two Part Additive. It also provides a useful supply of calcium and carbonates when correcting an imbalance in the aquarium.
Kalkwasser has unique characteristics making it useful as an additional supplement. It is used in conjunction with a protein skimmer as a means of reducing phosphate levels, and, given the high pH value, its use in helping to balance the potential acidification of the CO2 calcium reactor.
The CO2 calcium reactor is the most economical way of replacing calcium and carbonates in larger aquaria, or ones exhibiting a higher than average demand. It’s also the least time consuming method of the three.
From a personal perspective, I’m inclined towards a combination of methods as the need arises. A CO2 calcium reactor plus Kalkwasser, to prevent a tendency toward low levels of pH, makes very good sense. Add in the use of a Balanced Two Part Additive, but at a lower level than is needed to maintain correct levels on its own. You may find you can benefit from the pros of each of the methods, at the same time as cancelling out the cons.