An equipment that you should pay enough attention.

Yet it is one of the most important.

If we want to keep hard corals successfully, specially short polyp, also called SPS, we must bear in mind the following concept: stability.

And what is the stability? To begin with, some of which nobody talks very often but something that is very important. I often hear other hobbyists talk about the alcalinity level in their aquarium being very good, or that the nitrate level is very low, a few months ago they installed such powerful lighting fixture that all the fishes would need to swim with sunglasses. But there is something overlooked. They have to make adjustments in the calcium reactor every week because it ramps up or fall short, or do water changes in an inappropriate manner…or not never do them, which might be worse. And they wonder why those acroporas that had such a beautiful color time ago are now brownish and dull, or they even begin to die. Could it be that the parameters are not stable enough?

Think about a coral reef, one of the less evolutioned and primitive ecosystems (perhaps because there has been no need) in our planet. Is there any environmental feature that highlights? the answer is a clear YES, and I call it stability at medium and long term. Everyday the same photoperiod (or almost), temperature, salinity, pH, nutrients (that are mainly phyto and zooplankton, barely no COD, NO3 or PO4) and…the stars of the match: calcium and carbonates. This is something that corals really like because of evolutionary reasons (in other words, they have never lacked neither left over and so they have not developed any adaptations to compensate it).

There are numerous experiments and examples of aquariums in which nutrients levels and lighting were “far from ideal” but as long as they maintained stable carbonates and calcium , they would grow pretty corals, healthy and colorful; On the other hand, there are also many examples of aquariums with nutrient levels “perfectly” and lighting top-noch but not getting enough stability in the levels of calcium and carbonates which resulted in unhealthy corals and unattractive colors.

A succesful “Balling”? It is neither for price nor comfort, I think that it is because most of the aquariums that implement it exhibit beautiful and healthy corals. Again: a matter of stability.

Calcium and carbonate. Something to bear in mind.

Keep in mind that calcium reactors release calcium and carbonate ions (alkalinity) in a fixed and constant ratio (stoichiometric). When CO2 is used to dissolve the selected material, either aragonite, calcite, ARM or any other form of calcium carbonate, are released 10 ppm of Ca and 0,5 meq/l of CO3 (1,4ºdkH), this invariable ratio permits not to be necessary to test more than one of the two parameters (if we know that the carbonate risen a certain amount, we will automatically know how much the calcium has risen).

If we analyze this stoichiometric ratio we will soon understand why the alkalinity is far more important than calcium. We know that a coral can live perfectly within a calcium level between 380 and 450 ppm and a carbonate level ranging between 6.5 ° dkH and …say 9ºdkH (I know that many people maintain higher alkalinity levels and their corals seem happy, but I also know that there are people who live on burgers and beer and they are still alive and kicking). Figure out a typical starting point: the aquarium water has a calcium level of 420 ppm and an alcalinity of 7.5 °dkH. Imagine a lot of corals that are beginning to “eat” this soup of ions and we do not throw in any calcium and carbonates. In a few hours the level of Ca and carbonates will start to descend, a 1 ppm calcium is accompanied with a decrease of 0,14ºdkH. It slowly goes down until the alkalinity is out of range and corals begin to die (a coral that cannot calcify and grow, just dies, it's that simple). Notice that we only needed a drop of 8 ppm of calcium to get alkalinity out of range, the coral will not lack in calcium, but not having sufficient carbonates, it will be unable to build new cells from calcium carbonate and will die. And the same would happen with the upper limit in the case the reactor is “crazy” and release too many ions, alkalinity is always the first parameter that gets out of range.

In summary:

  • Calcium and carbonates are released (and consumed) in a stoichiometric ratio.
  • Carbonate is the first parameter that gets out of range

For these two reasons to adjust the calcium reactor it will be necessary to test the alkalinity.


Adjusting the calcium reactor .

It is not something to be done in a few minutes and it requires some patience, but once you have set it up, it will be months without doing the minimal correction, just fill in the media that is being consumed and monitor the CO2 used.

The adjustment is done in two stages:

Effluent alkalinity is adjusted by the CO2 supply rate

According to the product being used it will be advisable to fix a different pH setpoint; for example aragonite can dissolve perfectly with a pH of 6,7 while other stuff such as dolomite (that also incorporates magnesium carbonate) or ARM require a significantly lower pH. Fixing the pH setpoint we fix the rate at which the product is dissolved, but we should not start with very low values ​​because we risk blurring the water in the reactor (which will make a very abrasive mud accumulating on the pump rotor, accelerating its wear); it is therefore advisable to start with pH values ​​slightly higher and lower it until getting a good response in time.

No matter the mineral product we choose, We must aim for an alcalinity in the effluent water ranging between 30 and 40ºdkH. As a starting point we will adjust the valve to produce CO2 at a rate of 1 drop per second. The mineral product used in the the reactor will need at least 24 hours to reach a steady state that allows us to test the alkalinity value at the reactor outlet, with some certainty that it will keep constant.

We've surpassed 40ºdkH, just close the CO2 valve a little bit and test again after 12 hours, We are below 30°dkH, we open a little more gas, it is very simple. It is important to keep the alkalinity within this range if we want to optimize the consumption of CO2 and not to waste it.

Aquarium alkalinity is adjusted by fixing the effluent rate

Once we have the calcium and carbonates drip constant and within the range we are interested, it's time to adjust the aquarium alcalinity and calcium level. This is as simple as setting an initial drip (which it is usually about two drops per second) and test alkalinity every day until you get a minimum of three equal values. From this point on, we can consider that our reactor is set up but it is advisable to make regular checks, at least once a week.

Over the time we will feel confident that if the reactor is well adjusted and none of its elements is obstructed, the calcium and carbonates input will be invariable. However, if everything else goes well, corals (and coralline algae) will grow up and increase their uptake, so we must keep on testing alkalinity with some regularity.

I use to test it once a week, just before every water change. That does not prevent me to observe my millepora's polyp extension every night (can be done with any other SPS), and if I see that it has reduced I'll know that on the next day I'll have to do an alcalinity test. And I'll probably have to adjust the calcium reactor…