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(The following information has been supplied by a fellow hobbyist on the Internet who built this DIY project. If you have any questions regarding this project, then contact Kay Wilson.)

I know this is not a good sales tactic, but I'm sure that a lot of people will want to know how much such a system will cost before evaluating the system. So, I will just tell you and hope it does not scare you away because this system is so easy to care for and provides excellent results. Expect to pay between $230.00 and $330.00 for this system. Just so you know, most of this amount comes from the purchase of a dosing pump.

It is not the intent of this article to discuss the many different methods for maintaining calcium and alkalinity levels in reef aquariums. This article is simply my attempt to bring together some information I have collected over the years into one location. A lot of what I will present in this article is not original information. However, what is original is that all of the information is in one place. I have collected most of this information from various articles, books, and websites.

I have been adding calcium hydroxide a.k.a. kalkwasser to my tanks for years. Over the course of these years I have had ample time to experiment with different dosing methods. I have tried just about every method for mixing and dosing this substance. Dripping it with IV bags, reactors with powerheads, and evaporation condensation tanks, just to name a few. The method I will present has provided me with outstanding results. This method not only consistently and reliably allows the user to administer fresh KW in small doses while requiring very little maintenance but also, provides the user with a very effective means for controlling pH, maintaining the calcium level, and preserving the alkalinity. Before I start discussing the method there are a few topics that need to be addressed.

The first is the definition of kalkwasser. Kalkwasser is a saturated solution of calcium hydroxide. Calcium hydroxide is dissolved in freshwater, preferably RO/DI water, to make KW. About one teaspoon dissolves in a gallon of water. Fresh KW that has not reacted with carbon dioxide, which results in precipitated calcium carbonate, is what needs to be added. This is achieved by minimizing contact between the atmosphere and the KW solution.

The second topic is the evaporation rate of your tank. You will need to determine the evaporation rate of your tank. To do this you simply need to mark the current water level, allow 24 hours to pass, and then measure the amount of water it takes to fill back up to the mark. This rate will fluctuate throughout the year depending on humidity and the difference between your tank water temperature and ambient room temperature. Thus, allow a variation of +/- 10%.

The final topic to discuss before getting to the method is the duration, in hours, that the KW will be dosed. If a tank experiences wide pH fluctuations between the "lights-on" (high pH) and the "lights-off" (low pH) cycles then KW should be dosed only during the "lights-off" cycle, or for roughly 12 hours. However, if the tank does not experience wide pH fluctuations then KW may be dosed 24 hours a day. I would recommend dosing KW for 12 hrs during the "lights-off" cycle because most reef systems have enough photosynthetic animals to create a considerable pH peak during the "lights-on" period. If KW is added during this pH peak then pH values can reach 8.6 or higher.

Now it is time to get to the method. Below you will find a description of the system I use, details on how to design a system for your aquarium, and the materials you will need to construct such a system.

System Description

System Diagram

The system I use is modeled after the one developed by Alf Nilsen and described by Julian Sprung and J. Charles Delbeek in "The Reef Aquarium Vol. 1." The system has four parts: (1) the dosing pump, (2) the kalk reactor, (3) the magnetic stirrer, (4) and a freshwater reservoir. This system mixes calcium hydroxide with freshwater once a day in the kalk reactor. This results in fresh KW being dosed into the aquarium. This method works as such: The dosing pump pumps water from the freshwater reservoir into the top of the reactor. The out put of the dosing pump is matched to the evaporation rate of your tank. Freshly mixed KW leaves the reactor and drips directly into the aquarium or sump. The KW inside the reactor is mixed once a day by the magnetic stirrer. The reactor rests on top of the stirrer and the stirrer is on a digital timer so that it comes on 1-5 times a day for 1-5 minutes (see project notes). The top of the reactor is at least 4 inches above the water level it will be dripping KW into. This allows the KW to gravity feed into the tank or sump.

This system requires little maintenance. Once a week the top of the reactor is taken off and calcium hydroxide is added. About two to three times a year the reactor will need to be removed and cleaned. This is accomplished by pouring out the old water and washing out any sediment in the reactor. It is important to fill the reactor with water before putting the lid on. Since the lid is airtight, the reactor will only fill 1/3 full of water if the dosing pump is used to fill it while the lid is in place.

The Dosing Pump

The dosing pump needs to be a reliable pump that is capable of pumping your system's evaporation rate within 12-24 hours. The pump also has to pump this rate SLOWLY. I have used the "Reef-Filler" pump, the "Liter Meter" pump, and a peristaltic pump made by Control Company. Note: a float switch coupled with a power head does not work well because the power head is too powerful, making slow additions of KW difficult. Plus, float switches typically come on during the high pH cycle. Hence, when this method is used, too much KW is dosed at the improper time. In the long run, the pumps I mentioned above, or similar pumps, are the best option.

The peristaltic pump made by the Control Company can be purchased through VWR Scientific Suppliers, located here: http://www.vwrsp.com/. Search the catalogue for product # 54856-070. Also, the pump may be seen, but not purchased from here: http://www.control3.com/hpc2.htm. This is good pump that will work well for pumping 1 gallon a day or less. The other pumps may be purchased through any reputable on-line dealer such as Aqualink.

The Reactor: Description, Design, and Materials

Reactor Diagram

The kalk reactor is a cylindrical vessel, made of either 4 inch, 6 inch, or 8 inch PVC, where the calcium hydroxide is mixed with the fresh water. This vessel needs to hold a little more water than your tank's daily evaporation rate. To determine how large your vessel needs to be, first you need to determine how much water it needs to hold. It will need to hold 125% of your tank's daily evaporation rate. Note that the 25% takes into account the +/- 10% variance in your daily evaporation rate. Now, use this formula to figure out the size of the vessel you will need.

Example: Determine how tall a 6 inch container must be if the evap. rate is 1 gallon.

daily evap. rate = 1 gallon
1 gallon x 125% = 1.25 gallons
1.25 = [(6x6) x 0.8 x height]/231
1.25 = [36 x 0.8 x height]/231
1.25 = [28.8 x height]/231
1.25 x 231 = 28.8 x height
288.75 = 28.8 x height
288.75/28.8 = height
10.02 = height

Therefore, the equation indicates that the reactor should be 10.02 inches tall or, rounding up, 11 inches tall. However, an additional 2 inches will need to be added to compensate for the lid to the reactor. Hence, it needs to be 13 inches tall.

Materials list for making the reactor:

1. some 4", 6", or 8" inch PVC pipe
2. a piece of 1/4 inch acrylic large enough to cover the bottom of the pipe.
3. a length of 1/2 inch PVC pipe.
4. a length of 3/4 inch PVC pipe.
5. a 1/2 inch by 3/4 inch bushing.
6. a 1/2 inch 90 degree sxs pvc elbow.
7. a hole saw to drill a hole for the 1/2 by 3/4 inch bushing.
8. Weldon glue, found at your local plastics shop.
9. some epoxy putty, found at local hardware store.
10. some PVC glue and solvent.
11. a rubber test cap for the 4",6", or 8" PVC you are using for the reactor.
12. a piece of 1/8 inch plate glass cut to fit inside the 4", 6", or 8" PVC pipe. This piece of glass should be a snug fit, but not so snug that it cannot easily be removed.
13. inch 90 degree sxs pvc elbow.

To build the reactor cut the 4, 6, or 8 inch PVC pipe to length. Then glue the acrylic to the bottom using the Weldon glue. Clamp this in place and allow to cure for 24 hours. The base can be square or round. The important thing is to keep the base as small as possible unless you are building a really tall reactor. In which case you would want the base to be larger to compensate for the top-heaviness of the vessel. Next, place the rubber test cap on the top of the PVC pipe and mark how for down the cap comes on the container. Now, measure the diameter of the bushing and divide by 1/2. Measure down from the mark by this distance. Your goal here is to get the bushing as close to the top as possible without interfering with the fit of the rubber lid. Next, drill a hole using the hole saw at this new mark and check to see if the bushing fits in the hole. Make sure the 1/2" portion is facing out and the 3/4" portion is inside the reactor. If it fits glue it in place using the pvc glue and solvent. If it doesn't then file the hole until it fits and then glue it in place. After about 20 minutes, or however long it take the glue to dry, use the epoxy putty to further secure the bushing in place by forming a nice thick seal around the bushing outside of the reactor.

While the epoxy is drying, place the 3/4" elbow on the bushing inside the reactor. Next, cut a section of the 3/4" pvc pipe to fit inside the elbow and to reach down into the reactor about 2/3 of its height. DO NOT glue these pieces in place. Now, place the magnetic stirrer (see below) in its proper location and place the partly finished reactor on top of it. Next, use the 1/2" pvc elbow and pipe to configure a gravity feed from the reactor to your tank or sump. Since the top of the reactor is above the water level it will drip into, a gravity feed is made by simply using the 1/2" pipe and elbow to allow the water exiting the reactor to drip into the tank or sump. Note: (1) DO NOT extend the 1/2" pvc pipe into the tank's water. The water from the reactor MUST drip freely into the tank's water, (2) DO NOT glue the 1/2" pvc in place. You will need to be able to disassemble this configuration to clean and remove the reactor.

The Magnetic Stirrer: Description, Design, and Materials

Magnetic Stirrer Diagram

The magnetic stirrer is the devise employed to mix the KW. It has two main parts; (1) the stirrer itself and a magnetic stir bar. The kalk reactor rests on top of the stirrer and the stir bar goes inside the reactor. A motorised magnetic spins inside the stirrer causing the stir bar, inside the reactor, to spin. The result is a very efficient means for mixing calcium hydroxide with freshwater. Note: The piece of glass cut to fit inside the reactor serves to keep the stir bar from wearing through the acrylic bottom of the reactor.

Materials list: most electrical parts can be purchased from here : http://www.allcorp.com/.

1. 6-12VDC motor with a round shaft.
2. 9VDC 500 ma (for reactors less than 1 gallon), 9VDC 800 ma transformer (for reactors from 1-2.5 gallons), 9VDC 1300 ma (for reactors from 2.5-4 gallons).
3. Plastic box (project boxes work well, from Radio Shack etc.).
4. A magnet. Needs to be strong and about 1 1/2 inches - 2 inches long. The ones from Radio Shack are OK, but the ones out of magnetic algae scrapers are really good.
5. Pyrex stir bar. Go here: http://www.vwrsp.com/. Search the catalogue for product # 58948-488
6. Hole saw (you can use the same one used for the reactor).
7. Epoxy resin glue (five minute type).
8. Strapping tape
9. Piece of a 2" x 4" (a wood block). Needs to be as long or as wide as the plastic box.
10. Four one inch wood screws
11. A drill bit matched to the screws
12. A piece of 1/4 inch acrylic slightly larger than the top of the project box (optional).
13. Some solder.

Before you build the magnetic stirrer you first need to make sure that the magnet you have is compatible with the magnetic stir bar. Do this by letting the two items attach to each other. The stir bar should be fully attracted to the surface of the magnet that will be used to spin the stir bar. If the magnet pushes the stir bar away, at all, from the surface of the magnet then a new magnet will need to be selected. I wasted $10.00 on a bovine "cow" magnet before I tore apart my algae scraper. I can assure you that the algae scraper magnet works, and works well.

The first step is to cut the block of wood so that it fits snugly inside the plastic box. It does not matter whether it runs from front-to-back or from side-to-side. Now, draw an X on the wood block by drawing two diagonal lines from the corners (X). Where the lines cross, is the center point. Using the hole saw drill-out the center point. Set the block of wood aside.

In order to attach the magnet to the motor you will need to cut a small piece of wood that is the same length and width as the magnet. It should be about as thick as 2/3 of the motor shaft. Use the epoxy glue to glue the magnets to the piece of wood. Now, on a scrap piece of wood drill some holes to test for the proper size of hole needed to mount the magnet to the motor. This should be a tight fit. Once you figure out the size of the hole needed, drill this size hole in the center of the piece of wood glued to the magnet. Note: the center is found by drawing an X on the piece of wood. Set this aside.

Now, get the block of wood (from the first step)and cover one side of the hole with the strapping tape. Poke a hole in the center of the strapping tape just large enough for the shaft to fit through (you can find the center by using the piece of wood that was cut out to make the hole). Insert the motor so that the motor is inside the hole with the shaft sticking out of the hole in the tape. Now mix-up some epoxy resin glue and fill in the hole around the motor. Try to get the motor as centered and as level as you can get it. While the glue is drying turn your attention to the plastic box.

You need to drill a hole in the box large enough for the wire from the transformer to pass through. Cut the plug off of the transformer, if there is one, and run about 12 inches of the wire inside the box and then tie a knot in the wire at the 12" mark. Separate the wires and strip about 2cm off the ends of each wire. Note: if there is a green wire (ground wire) just fold it over. Now, get the block of wood with the motor in it and glue the magnet to the motor shaft trying to get it as level as possible. After the glue has dried solder one wire to each lead on the motor. It doesn't matter which wire goes to which lead. Finally, center the block of wood in the box. Secure it in place with the wood screws, two in each end.

Now put the lid on the box and make sure that everything works as it is supposed too. If your box needs it, use the piece of acrylic to reinforce the lid. It can be screwed or glued on. Note: I tried to use aluminium for this purpose, but it interfered with an electrical field.

Now that you have the reactor and magnetic stirrer built you are almost finished. All you have to do now is locate the freshwater reservoir somewhere close to your tank (in the stand hopefully). Once the reservoir is in place, you need to locate the dosing pump so that it pumps water from the reservoir into the reactor. To join the doing pump to the reactor simply drill a hole in the rubber top just large enough for the tubing from the doing pump to squeeze in. Remember, that you want this union to be as airtight as possible, so the snugger the fit the better.

Now you are ready to adjust the doing pump to match the evap rate of your tank. Depending on the pump you selected this probably means simply turning a knob or two. Once you have the evap rate matched you are ready to start adding calcium hydroxide to the reactor. Simply lift the rubber lid off, make sure the glass bottom is in place and drop in the stir bar. Next, add one teaspoon of calcium hydroxide per gallon of water, in the reactor, plus, one teaspoon for every gallon of water that will be evaporated from your tank in a weeks time. For example, if your reactor holds 1.25 gallons and your tank evaps 1 gallon a day, then you would add 8.25 teaspoons of calcium hydroxide. This will last for 7 days, and then 7 teaspoons will need to be added. Note: you would only add the extra 1.25 teaspoons after cleaning the reactor or anytime that the water in the reactor has been replaced by any means other than normal operation.

Freshwater Reservoir: Description, Design, and Materials

The freshwater reservoir is any container that will hold a given amount water. You will be using it to hold the freshwater that will be dosed into the reactor. If you can make it big enough to hold a week's worth of water I think you will be very satisfied with the results. This container can be anything, mine is a 15 gallon high aquarium. Also, if you have a RO/DI unit you can hook it up so that it automatically refills the freshwater reservoir. This is a REALLY nice feature because it will allow you to use a small freshwater reservoir and will relieve you of a maintenance task. However, plumbing might be difficult.

While I'm on the topic I might as well add another option as well. You don't actually have to use a reservoir if you have a RO/DI unit and a float valve. The float valve goes in the sump and is connected to a timer. The RO/DI unit is attached to the timer and is connected to the reactor. The timer only allows the RO/DI unit to operate during the time you specify. This is a handy way to use your RO/DI unit and the unit itself does not have to be located in the tank stand. The pressure switch and solenoid(the two parts of the float switch) may be separated so that you may locate your RO/DI unit in a remote location. If you own a SpectraPure you are in luck because you may call them for more details on remote installation. Note: This method may require you to purchase a larger membrane for your RO/DI unit.

Project Notes

1. The programmed settings of the digital timer for the magnetic stirrer will greatly impact your tank's pH and calcium levels. I suggest starting the implementation of this method as follows. Set the dosing pump so that it turns on 1hr after the lights go out and turns off 1-2 hours after the lights come back on (total of about 12 hrs this makes the math easy ; ). Set the timer for the stirrer to come on for five minutes, one hour before the dosing pump turns on. If this does not provide the desired results, then try this.
   Program the magnetic stirrer's timer to turn the unit on for one minute during the midpoint of the dosing pump's "on" cycle. If you still experience pH fluctuations and low calcium levels then reprogram the digital timer again. This time have it come on twice, one minute each time. Follow this process until the desired results are achieved. IMPORTANT NOTE: the time-frame of the above process is weeks not days, i.e. make a change wait a week.
2. The amount of calcium hydroxide (one teaspoon per gallon) described earlier is simply a rough guide. This measure is intended to give you a good starting point. You will need to adjust this amount based on several factors, each of which will be different for every reef tank. One of these factors is dependent upon how you operate the reactor. If you dose suspended Ca(HO)₂ then chances are you will need to add more Ca(HO) ₂ than one teaspoon per gallon.
3. Example(my system): I have a 120 gallon tank. My evaporation rate is about 1 gallon per day. I add 3/8 of a cup of calcium hydroxide every 10 days or so to my reactor. My dosing pump is set to pump for 12 hrs. It turns on one hour after "lights-out" and turns off one hour after "lights-on." My stirrer turns on for five minutes, one hour before the dosing pump turns on. Then, 1/3 of the way through the "lights-off," the stirrer turns on for one minute. then 2/3 through the dosing time the digital timer comes on again for one minute. I have found that this combination of timing and amount of calcium hydroxide provides my tank with great stability. My calcium and alkalinity are always at or above natural sea water values and my pH range is 8.17 - 8.27.
4. I have played around with my pH values by using my reactor to control my pH. I found that my corals exhibit better polyp expansion in the pH range of 8.17 - 8.27 than in the range of 8.27 - 8.37. You may experience something different.
5. Someone asked the question "Does the reactor have to hold the evaporation rate?" I responded, "I have never really thought about but, I guess you could build a reactor that holds 1/2 of your evaporation rate. Then you could program your timer to turn on half way through the dosing cycle. This way you would be mixing two batches of KW per day instead of one. Please note that if this is done undissolved Ca(HO)₂ will be dosed(unless you get a digital timer for your dosing pump and have it turn the pump off for one hour while the KW is mixing and settling). This is not necessarily bad. In fact, I purposely stir-up the undissolved Ca(HO)₂ twice, for a total of 2 minutes, during my dosing cycle so that I may add undissolved Ca(HO)₂ to my tank. With my evaporation rate and calcium demand I have found that this is what my tank needs. Yours should be different."
6. Most important, Have fun!! And if you have questions direct them to my e-mail: .

Completed Units

If you have built one of these units, then please send me (Dr DBW) some photos to put up here for others to see your handy work.

Rhino

Completed calcium hydroxide reactor

View inside the reactor, showing the magnetic stirrer bar

Magnetic stirrer

Magnetic stirrer motor

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