By Richard Aspinall

Richard runs through the basics of setting up this often confusing bit of kit

Images: R. Aspinall

There are several ways to maintain the levels of calcium, alkalinity and magnesium within our systems. The ‘Big 3’ as they are often known, are the parameters that we need to monitor most closely and maintain with the minimum variation, if our corals and many other calcium-using animals are to grow and prosper.

Direct dosing using pre-mixed liquids, Balling systems and Kalkwasser stirrers are employed by many with the latter falling out of favour somewhat in recent years. Balling methods are increasingly common in Europe, though from what I’ve read, calcium reactors still hold sway in the US.

So what are these techniques trying to achieve? In essence we need to replenish the chemical elements in the water that the growth processes of hard corals, clams and other inverts along with calcareous algae are removing from the tank water as they lay down their own skeletons, shells and so forth. In the oceans a range of geological processes ‘tops up’ the chemical balance including run-off from eroding rocks on land. In a closed system like an aquarium the hobbyists needs to take action.

Calcium reactors are very straightforward in principle. Dead coral skeletons (calcium carbonate in the form of aragonite), crushed into small pieces, are dissolved and the elements and chemicals they contain are released into the aquarium water and are available for uptake by the aquarium inhabitants to make new skeletons. Fairly simple in theory: as the coral gravel dissolves it releases elements in the correct proportions. In principle, if the alkalinity of the water in the aquarium running a calcium reactor is within the usual 7-10dkH range then the resulting calcium and magnesium levels should be correct also (in practice this is rarely the case – see the troubleshooting section). A calcium reactor provides a balanced addition of calcium and carbonates (that contribute to alkalinity), one cannot alter one parameter without changing the other. However, systems with very prolific coral growth may require additional inputs of calcium, in fact I have visited several systems that us a kalkwasser stirrer as well as a calcium reactor to provide enough calcium. As with anything in this hobby, there’s always more to learn after the basics!

How does a calcium reactor dissolve the coral media?

Again, this is straightforward in principle, a small amount of carbon dioxide is drawn into the reactor vessel, through valves to control the flow. The CO2 dissolves in the water inside the reactor to produce a weak acid, which dissolves the coral skeletons. As water is continuously running into the reactor from and then into the aquarium, the water exiting the reactor (effluent) returns to the tank richer in dissolved elements. Usefully it is also richer in certain trace elements that the dead corals took up in their lifetimes as well.

In practice we can tune the pH of the calcium reactor by controlling the addition of CO2, more CO2 means lower pH and less, a higher value. To do this a pH controller is essential. A pH probe is fitted into the reactor and the controller set to generate a pH in the reactor of around 6.5. If the pH falls below this level the controller shuts off the CO2 flow using a solenoid operated valve on the CO2 source bottle and when the value begins to rise the solenoid valve is opened once more. pH controllers are not always used, but I would consider one a worthy investment to ensure the acidity level in the reactor is kept low enough to dissolve the media but also not too low as to adversely reduce the pH value in the main tank.

Let’s look at the kit…

CO2 bottle and regulator

Here we see the regulator/valve/solenoid assembly. When powered the solenoid has a small indicator light. The needle valve is upper left.

CO2 is a colourless, odourless gas that when combined with water forms carbonic acid. It’s the same stuff that erodes old statues and creates limestone caves. For our purposes CO2 is provided in small pressurised cylinders which tend to be single-use. Hobbyists with large systems often find that they achieve better overall economy by using large industrial cylinders which they can get refilled.

The CO2 flow is regulated by a valve with two gauges, one tells us the bottle pressure and the other the operating pressure. A regulator inside the valve keeps the operating pressure at correct level as the overall cylinder pressure drops, which is essential to avoid over or under dosing.

Attached to the main valve/regulator is a solenoid controlled valve which requires a mains plug connection. This is a safety feature that means if the power fails the solenoid shuts the valve and the CO2 is contained. Its other use is with a pH controller allowing the CO2 flow to be turned on and off as required and as noted above. Attached to the solenoid is a needle valve for fine control of the CO2 output. In practice needle valves can be tricky to set just right so I prefer to use an extra in-line air valve for fine tweaking. A one-way valve attached into the CO2 feed line is a good idea also.

I’m using TMC equipment for this article and I’m grateful to TMC for sending it over, but please note that whatever regulator, CO2 source and solenoid your use, they all work in the same basic way. Though if you’re buying this kit in a UK fish shop, the chances are you may well be buying TMC equipment.

The Reactor

This compact design of reactor is different to many larger models. The left hand input takes CO2 and the pH probe can be seen fitted into holder in the centre of the top plate. To the right is the inflow feed. In this model the circulation pump is at lower right and if you look carefully you’ll see the CO2 inflow pipe running down and into a chamber at the very bottom left.

Calcium reactors vary greatly in their design, ease of use and durability and of course price. They also come in various sizes and need to be chosen according to the needs of your tank, now and in the future, when it’s full of Acroporids and Tridacnid clams growing like crazy (hopefully).

The reactor is filled to the recommended level with the media and then attached to a source pump. This can be done by taking a feed from an existing return pump, for example, by inserting a T junction into the pipe, with a reducer small enough outlet to allow airline tubing to be fitted that then attaches to the reactor inlet. A better solution uses a dedicated peristaltic pump that provides the small amount of regular flow needed. Peri pumps can also produce a decent pressure to force water into the system.

Some compact reactors such as this model – which TMC say is their best seller at the moment- are designed to work without a dedicated feed and use their internal circulation pump to draw in aquarium water. Water in the reactor chamber is circulated by a pump which also serves to thoroughly mix the CO2 into the water as it passes through it.

Bubble counters are essential, they allow you to see how many bubbles of CO2 are entering the reactor over a given period of time. Many units have external bubble counters, though this reactor has a slightly harder to see counter built-in to save space. Similarly, another chamber shows us how much water (in drops) is entering the unit, with a valve on the output allowing us to control this setting as well. Not all reactors have this feature and just rely on you counting the drops out. External bubble counters are best filled with RO water and not aquarium water – as the liquid evaporates they can become clogged if salt water is used.

In essence we have all we need. Circulated water, controlled CO2 input and a controlled water output.

The pH Controller

This handy piece of kit takes a lot of trouble out of running a calcium reactor. Once calibrated, the probe is inserted into the reactor (most reactors can accommodate a probe nowadays) where it monitors the pH of the water in the reactor. A value of 6.5 is recommended to dissolve the media with ease.

The controller is set to ‘come on’ and activate its power socket to open the solenoid valve when a value of say 6.9 is reached and turn off when the pH reaches 6.5. In this manner the reactor will always be at the right pH and if and when you adjust the flow rates the reactors pH will remain correct.

Using a pH controller means that you can avoid the tedious checking of the effluent pH and allow the controller to do the work for you. You will need to set the controller to the upper and lower values, most are very easy to adjust and set.

Setting up

This is how I do it, but everyone has their own method.

1. First, assemble your kit. Make sure you can access all the valves and controls with ease. Once you are familiar with your reactor you might be able to stow some of the bulkier components such as the CO2 bottle out of the way, but to begin with make sure all is easy to reach – you will no doubt be doing a fair bit of tweaking. Make sure you’ve rinsed everything and cleared any residues. Rinse the media to remove dust and particulates that may block the pump and pipework.
2. Charge the system with water using whatever feed pump option you choose, watch carefully for leaks, incorrectly seated O rings and pipework that may work loose. Some reactors such as this one will need to be filled with aquarium water by hand in order to prime it. Carefully look over the plumbing and make sure it won’t be easily disturbed and cause leaks when you carry out maintenance and cleaning.
3. Once you’re happy that there are no leaks and the reactor pump is running well, turn the rest of the kit on. Make sure your pH probe is calibrated and the controller set to ensure a value of around 6.5. (I’d recommend setting it to come on when the pH is at or above 6.9 and then off when it reaches 6.5). Now you can carefully open the needle valve to allow the CO2 to flow. Set it to around ten bubbles per minute – you can fine tune it later using an extra in-line valve if you’ve added one. And adjust the outflow (effluent) to 30-40 drips per minute, again you can fine tune later.
4. You will now need to monitor the tank closely. Leave the reactor to settle in and check the parameters after several hours. If the alkalinity in the main tank rises unduly reduce the amount of CO2 being added or increase the drip rate of the effluent and if the alkalinity is too low increase the CO2 input or reduce the amount of effluent. Whatever changes you make, make sure they are very small, fine tuning can take many days, but you will get there and you need to avoid shocking your livestock.

It is a good idea to record the changes and note the trends and check regularly over time especially as the media runs low or coral growth increases.

Troubleshooting

Low tank pH

This is a potential problem that many hobbyists encounter, when the effluent leaving the reactor lowers the overall tank pH. Thus is due to the reactor adding bicarbonates which lowers the pH until the CO2 is degassed into the air around the tank. Adding sodium bicarbonate as a buffer has the same effect.

There are several things to try here: firstly, ensure the effluent is dripped back into an area of good water flow to boost degassing. Secondly, try piping the effluent through another chamber filled with calcium carbonate based media (perhaps coarse coral sand). Many reactors these days have extra chambers for this purpose, though some people make their own from old plastic pop bottles filled with coral gravel. You may also try dosing kalkwasser to raise the pH.

Balancing calcium with alkalinity

In principle a calcium reactor is dosing the correct ratios of carbonates (alkalinity) and calcium, but if calcium is being depleted rapidly by coral growth attempting to increase the reactor’s output to compensate will cause the alkalinity levels to rise as well.

Annoying this might mean having to manually dose calcium in the form of calcium chloride either as a drip or through a klakwasser stirrer or perhaps via top up water.

Safety

CO2 can be risky if not handled carefully. Ensure your system is set up to allow good ventilation to ensure that CO2 degassing from the tank can escape easily. Due to it being denser than air, CO2 can ‘lurk’ in the bottom of a cabinet and exclude oxygen thus limiting the amount of oxygen available for exchange into the water. Systems that are very confined or sealed may be affected.

This is also why a solenoid is such a necessary device, stopping gas flow in the case of power outages.

So that’s it…seems simple right? Well it might be, it might not. Tinkering with calcium reactors occupies many aquarists for many hours, but when tuned just fine, then the results are well worth it.

I hope this brief introduction to the basics and the equipment used has been of use. As I always recommend, do more research. Just about everyone who has ever owned a calcium reactor and written about it will have their own take on the subject so it’s worth getting some more opinions.

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