How to use kalk in your auto top off


Kalk is one of the simplest and yet most confusing things a lot of folks considering adding to there tanks so I figured it would be handy to write a how-to on using it in my preffered way, an auto top off. For anyone interested in implementing kalk it should help you figure out what it is, how to mix it, and how to address any concerns about using it. Even a few pointers on auto top off selection if you think you may run kalk in the future!

First of all, a little background on kalk for those who don’t know what it is and what it does. There are a lot of different names for what folks commonly refer to as “kalk”. Kalkwasser, kalk water, kalk, lime water, CaOH, lime, pickling lime, and even more! These all refer to the same thing which is for all intents and purposes Calcium Hydroxide or Ca(OH)2. The wide variety of names seems confusing but they actually all come back to the same thing. The term “Lime” in this sense actually derived from the same place as lime stone (stone that is largely Calcium Carbonate, the same thing as coral skeletons). We commonly borrow things from the Germans in this hobby, and this is no exception. “Kalk” is German for lime, wasser translates to water. So “kalkwasser” actually translates directly to “lime water”. Usually “kalk” refers to the dry powder and “kalkwasser” the mixed solution but folks tend to use either interchangeably.

Kalk is a really handy tool to for maintaining calcium and alkalinity for a variety of reasons. First of all, the kalk itself is pretty cheap as far as reef supplements go. A gallon of the stuff goes for less than $15 bucks. While I’m getting ahead of myself in terms of dosing, at the max dose of 2 teaspoons per gallon you’re looking at 384 gallons of fully saturated kalkwasser per gallon of dry kalk.

Generally speaking kalk is pretty easy to implement. If you already have an auto top off system that adds top off water in small bursts, it really is as easy as pouring a few teaspoons into your top off container and giving it a few mixes. If you don’t have an auto top off system you have the added step of installing one, but that is simple as well and you were going to do that anyway right? The following instructions assume you already have an auto top off, but if not I will include a few pointers at the end for selecting a good option.

Kalkwasser is about the only solution you can add to your aquarium that has both calcium and alkalinity together in one solution, and won’t just precipitate out before it’s added to the aquarium. Not only does it supplement both your calcium and alkalinity, but because it’s a single solution it forces you to dose them in a matched amount. You can’t accidentally get your calcium and alkalinity out of balance like you could with separate supplements.

Lastly, and this could be a benefit and a curse, kalk has a pretty drastic pH raising effect. A lot of folks are concerned with the pH of their tanks and while in 99% of cases it’s not really something to be concerned about (it’s usually pretty hard to get your tank out of a safe pH range without trying). If your pH is already on the high side, kalk may not be a great option as it will raise it further. But if it’s on the low side it will help bring it up a bit. There is a danger here as well though. If you were to overdose and add too much kalk to the tank it could be catastrophic to the tank. There are ways to mitigate this risk and I will touch more on this at the end of this how-to.

Adjusting Levels:
Before you start dosing kalk, you need to get your calcium and alkalinity to the proper levels. You do NOT want to use kalk for this purpose. The pH effect of kalk is significant and while it works great for maintaining calcium and alkalinity levels, adding enough at once to actually raise the levels is a good way to send your pH skyrocketing. There are two common methods. The first is to use water changes. This method is only suitable if you can do enough water changes, of a significant amount to raise your levels to acceptable amounts. If you have a new tank or even an old tank that is low in demand, this is likely your option. Simply test your water parameters after doing a normal water change, if the levels are where you want them afterword’s your good to go. The larger and more frequent the water change, the easier it will be to use this method (and this assumes you have a salt mix that mixes up to your desired levels). If you can’t, or don’t want to, adjust your levels via water changes then using a two part solution is the best for the job. These allow you to simply pour in a calcium solution to raise calcium, an alkalinity solution for alkalinity and so on. This is my preferred method as its quick, straight forward, and handy for when you need to make the occasional adjustment in the future as well. Considering you’re going to need to dose magnesium separately as it is, might as well pick up a small kit.

Mixing Kalk:
To mix up your kalkwasser you will need your top off container, a mixing spoon, and of course your dry kalk powder. A little bit of kalk goes a long ways here and it will reach its maximum saturation at only two teaspoons of kalk powder per 1 gallon of water. Keep in mind that is the max dose, most folks will use much less. When first starting out with kalk I would highly suggest starting with only about ½ teaspoon per gallon of water. As you dose the kalk monitor the calcium and alkalinity levels and if they are declining, then you add a bit more in your next batch. The pH in your tank is going to change when you switch to kalk, and the more gentle the transition the better.
Start by filling your top off container up with RO/DI water. Then measure your dry kalk powder (recommended to start at 1/2 teaspoon per gallon of water, max dose of 2 teaspoons per gallon). Pour the powder into your top off container and gently mix with the spoon. It doesn’t take very vigorous stirring to mix the solution and the kalkwasser solution has a pH over 12 when it’s fully saturated, so you don’t want it sloshing around on you or your stuff.

After mixing for a minute or two, move your auto top off container to its normal location and allow the solution to settle. Usually the solution will be a bit cloudy but that is perfectly normal and nothing to worry about. Also, don’t keep mixing it! Just let it be! I know you want to, but don’t! Kalkwasser reacts with the CO2 in the air and it will render the kalk unusable by reactor and forming calcium carbonate (which won’t dissolve back into calcium and alkalinity in the aquarium). If the solution is not constantly aerated it will form a crust over the top and it will actually last quiet a long time (over a month). Hook a powerhead up to it and keep it aerated and you’ll be lucky to get a day out of it.

Now you can go ahead and connect your auto top off. A few tips on that. First, make sure your system is full. You don’t want your auto top off to kick in and dump a gallon of kalkwasser into your system because it was low when you put it on. If it is low, top off with plain top off water first. This way the kalkwasser is added slowly with normal evaporation. Second, if your auto top off uses a submersible pump position it an inch or two off the bottom of the container. If it has a tube it draws solution up from, keep the input of the tube an inch or two from the bottom. This prevents the ATO system from drawing up the sediment on the bottom of the container. This is not only going to be bad for your pumps, but adding slurry of kalk powder/kalkwasser to the tank will be super concentrated and have a much more significant effect on the pH.
Technically you’re done, this is all that is required to actually run kalk in your auto top off. When the container is empty, just repeat the process. You don’t have to empty out any sediment each time but I would do it at least once every other fill just to keep it clean.

Because of the high pH of kalk there is one additional measure I would always recommend. Using some sort of pH controller on the system as a safety backup. This would basically be configured in the opposite way of a calcium reactor. Here we would want the controller to allow the auto top off to function as normal unless the pH was to go over a safe level (say 8.5 for example). I would set the cut off .1-.2 higher than the pH normally is while you’re running kalkwasser. This way the auto top off is left to do its own thing, unbothered, hopefully 100% of the time. The only time anything would happen is in the event of an accidental overdose or some other circumstance where the pH exceeds the maximum range (the pump stays on by accident, something else raises the pH, etc.). In this event the pH controller would cut power to the auto top off system and stop the pump for adding more kalkwasser/further raising the pH.

If you already have an aquarium controller like a Neptune Apex or a Digital Aquatics Reef Keeper, you may need a part or two but they are certainly capable of doing it (and the most packages include it right off the bat). If you don’t have and don’t want a full aquarium controller, a standalone pH controller like the Pinpoint pH controller or the Milwaukee pH controller will do the trick to. Just make sure whatever you chose has the ability to turn the outlet on when the pH is lower than the setpoint (both of these units do that). Many other pH controllers were sold for calcium reactors which function in the opposite direction (outlet on when the pH is ABOVE the setpoint). Some are dual function, some are not. Setting up the pH control helps address two issues at once. First of all it will help prevent the catastrophe or a massive spike in pH. Secondarily it may also prevent your auto top off from overfilling/flooding or continuing to add water in the event of a water leak. As the water leaks it would require more top off than normal, which would cause the pH to increase more, and thus cutting off the supply of top off (at least until the pH drops back down).

Choosing an auto top off for dosing kalk:
Obviously you can’t dose kalk in your auto top off if you don’t have one J If you’re looking for one to use with dosing kalk, there is a few things that can make some models better or worse than others, though it depends on your situation. Most of it boils down to the fact that you want an auto top off system that will add less water, more frequently, than the opposite. That way you are minimizing any spikes to the pH and it should remain fairly stable. You also would be best served by a system whose pumps are inexpensive and fairly easy to replace as its likely they will have a shortened lifespan used with kalk. My preference is for the Tunze Osmolator 3155 for this purpose for a couple of reasons. First of all, when the optical eye detects the water has dropped, it will add a minimum amount of water and raise the water level back to the sensor. This is fairly sensitive and not something that is going to raise the water level 3” at a time. It also has an emergency backup float that is close to the optical sensor so should it fail, it won’t dose as much extra kalkwasser as an ATO unit with a timer backup, for example. Lastly the pump is easy to replace and inexpensive (less than $25).

I would generally try to avoid ATO systems that have a high and low sensor where the ATO system turns on when it goes below the low sensor and continues to pump until it reaches the high sensor. These systems have their upsides in some situations as they prevent the pump from short cycling, constantly turning on/off multiple times in a second (mostly related to single float switch systems, units like the Osmolator already address this). The downside is that the sensors usually have to be far enough apart that they end up adding a lot of top off water in a dose. The amount added can be reduced by moving the sensors closer together, but if you get to close you can run into issues as well. These systems also take longer between cycles as you have to wait for water to evaporate before it drops to the lower sensor.

The Osmolator happens to be my choice for this situation but as long as you have something that will address small changes in water level and has a pump that is easy to replace you will be in good shape. The first time you setup your auto top off I would recommend running it with just water (no kalk) just to make sure its operating correctly and didn’t miss any steps. Your tank will deal with an extra gallon of water a lot better than an extra gallon of kalk!

Let me know what you guys think, do you guys use kalk in your systems? How often to you mix it? Let me know in the comments below:

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