I had a member request some information on kalkwasser and Nilsen (kalkwasser) reactors. Basically, how they work, what they do, why people use them, how to use them, etc.
I'll offer the information that I can - please feel free to jump in!
First of all, kalkwasser is a German word for lime water. Kalk (powder) is basically calcium hydroxide - you mix it with RO/DI to introduce it to the aquarium. Kalkwasser is considered a "balanced" additive, in that is maintains/adds both calcium and alk equally.
Other benefits of kalkwasser are that it precipitates phosphates, and it also raises the pH level of the tank.
Another benefit is that is can be a relatively inexpensive way to maintain ca/alk in a reef tank.
Many people drip kalkwasser manually. This is done by mixing approximately 1 tablespoon of kalk powder per one gallon of water. Stir/agitate well, and let this sit overnight. You would then pour off the clear water at the top of your container into some sort of dripping or dosing container.
Many people use IV line to drip their clear kalkwasser solution.
It is important to drip kalkwasser, rather than to add large amounts at one time - because of the high pH of kalkwasser (12.0 - 13.0), it can cause significant and harmful shifts in the pH if added to rapidly.
How much kalkwasser to dose?
Most people dose kalkwasser to replace all evaporated water.
When to dose?
Many people drip kalkwasser only at night, as this is typically when pH is lowest. If stable pH conditions in the tank allow for it, it can be dripped 24/7.
Nilsen [Kalkwasser] Reactors
Nilsen reactors are just a convenient way to dose kalkwasser. In most cases, it is pretty simple to rig up some sort of dosing container and tubing to manually drip kalk. Some people (like us!) opt for more convenience. The main reason we decided to use a Nilsen reactor was due to the amount of water we evaporate - up to 5g/day. Since we're away for many long weekends (and sometimes a week or more) on vacations, we searched for a more convenient way to dose Kalk. The Nilsen reactor is it.
The Nilsen reactor is basically an acrylic tube which contains RO/DI and kalk powder. Some models use magnetic "stirrers" - ours is simply connected to a Mag pump on a digital timer. The timer is set so that it turns on for 15 minutes every 4 hours.
Our RO/DI is plumbed directly to the Nilsen reactor, so we drip kalkwasser constantly, 24/7. We use a valve to adjust the drip rate.
Maintenance consists of adding a "bunch"
of kalk powder (8-10 tbsps?) every two-three weeks. We've had the Nilsen reactor up for about 6-7 months now, and have had to replace the impeller in the mag pump once.
Here are a couple links for DIY Nilsen reactors:
JJ Geisler's DIY page - includes 3 Nilsen Reactor plans< >Nilsen Reactor, Bill Esposito< ]>The Mantled Monster Nilsen Reactor page<
Hope this is helpful!