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Nicolas Will - Nilsen Reactors

By Nicolas Will. Posted to Reefkeepers emailing list, Thursday 6th May 1999.

I won't go into discussing which reactor is better (Calcium carbonate/CO2 or Nilsem). But I'll say that a Nilsen Reactor is *by far* better than dripping.

Why ?

When you mix kalk, you get a solution with a very high concentration of Ca++ and OH-. Thus it is very basic, around pH 12.

The problem is that is will react very easily with dissolved CO2 already in the water or coming from the air/water interface.

The result is that Ca++ will react with CO2 and give calcium carbonate, insoluble and useless for what we want to do. Also the pH will drop very rapidly.

So, when you drip, the results are good at the beginning, and are getting worse and worse.

After an hour or so, your drip is virtually useless, not a lot of Ca++ added, a lot of calcium carbonate that will form useless sediments.

So rapidly we are wasting resources and energy. This can be OK for small or lightly loaded systems, but don't hope to maintain Ca levels in big loaded tanks with that. You will notice that it will also be difficult to maintain good alkalinity with this method, even if the theory tells you it's possible. That's why most turn to the other type of reactor after some time.

So, what are the options ?

Make very small amounts of kalk each time you want to drip ? Making kalk and dripping is already a pain, what if you have to do it even more often ?...

Find a system that is hermetic to air ? why not, but then your drip will be difficult to maintain.

One other drawback of dripping or dosing is that either you add too much or not enough compared to evaporation.

Now, what is a Nilsen reactor ?

It's a tube where make-up water transits. That tube is hermetic to air, thus to CO2, so no reaction. That tube is also equiped with a system to mix calcium hydroxide to the water (usually magnetic stirers or pumps) regularly during the day.

What does it do in fact ? It just mixes fresh kalk every time you need it. It is hermetic, and as it work with a top-off system (usually working with a float switch), it will add exactly the needed amount of water.

As fresh kalk is added every time, you will be able to sustain high calcium demands and also maintain alkalinity.

Settings are more than easy : adjust the number of times you want to use the mixing system depending on your needs.

Maintenance is low, once every 2-3 weeks just add a few spoons of calcium hydroxide inside the tube.

There are few reactor like that on the market. The only one I know is from Ratz. I don't know how easy it is to find it outside Germany or Europe. But anyway, one is very easy to build. It's basically a tube and a very few pipes. You don't need an engineering degree to make it. Tools are also kept to a minimum : glue, a drill, and a saw. You can build one in 20mn.

The only tricky part was the mixing system. Magnetic stirers are a bit expensive or not easy to build for the inexperiences, and anyway have some problems : the tend to wear down the bottom of the reactor, giving leaks and forcing you to change the bottom part regularly (even when using glass plates), and created places where a calcium hydroxide paste formed and wasn't mixed. Water pumps are OK, but with square bottoms, the same paste result was there.

The solution that looks simple when you see it it to use a spherical bottom and a powerhead for mixing. No more paste problems, no wear, and an easier and cheaper way to mix.

Even if I said that I wouldn't compare the kalk-reactor with the CaCO3/CO2 reactors, I will a bit...

  • This system is *cheap* (no expensive CO2 system)
  • as it is very efficient, it can compare in terms of capacity
  • alkalinity levels are kept at a more natural level
  • no danger of playing with CO2 in your tank
  • very safe, but some experienced Ca saturation problem in their big loaded tanks nevertheless (precipitation snow fall, not very dangerous, but a bit irritant to corals, and a pain to clean). So at the beginning don't mix too often and watch your Ca level.

Original in French:

Original in English but less details but with lots of pics:

On my site:

Created by liquid
Last modified 2006-11-24 18:41