|TEXT, PHOTOS AND DIAGRAMS BY SANJAY JOSHI|
CaCO3 + H2O + CO2 <——> Ca2+ + 2HCO3-
So, the calcium carbonate reactor is basically a device that brings the three ingredients — water, CO2 and calcium carbonate — together in a manner so as to allow efficient production of HCO3- and Ca++ ions. All reactor designs basically follow the same principle, but differ in the techniques to create the circulation loop, the manner in which CO2 is injected, how the water is input to the reactor, and how the effluent is drawn off. We will just stick to the basic principles and look at building your own reactor.
The most common reactor design that is currently used is the closed recirculating reactor. In a recirculating type of reactor (also called the Löbbecke reactor, described by Hebbinghaus 1994), the mixture of CO2 and H2O is continuously circulated in the chamber through the calcareous media in a closed circulation loop. Water from the tank/sump enters the reactor through an inlet and exits through an outlet, both of which are connected to the main recirculation loop. Typical recirculation rates are in several hundred gallons per hour, while typical input/output rates are in few liters per hour (L/hr). Water entering the reactor comes in at tank alkalinity levels and effluent leaving the reactor has a much higher alkalinity (depending on the settings).
|Materials List for Mixing Chamber Assembly|
|1||4½-inch OD 1/8-inch
24-inch long acrylic tube
|2||4-inch PVC closet flange
with test cap
|Local Hardware Store (LH)||1||$5|
|3||4-inch PVC female
(FNPT* x Slip)
|4||4-inch PVC cleanout plug
with male pipe thread
|5||½-inch PVC male adapter
(MNPT** x Slip)
|6||½-inch PVC pipe "legs"
(cut from PVC pipe)
|7||Egg crate —
5 inches x 5 inches
|8||Fiberglass window screen mesh
(1 square foot)
|Materials List for Re-Circulation Loop|
and Input/Output Connections
|9||½-inch PVC union
(Slip x Slip)
|10||½-inch PVC elbow
(Slip x Slip)
|11||½-inch PVC Tee
(Slip x Slip x FNPT)
|12||Tubing adapter —
elbow ½-inch MNPT x ¼-inch barb
|13||¼-inch needle valve for water||ALS||4003-002-A||1||$32.80|
|14||Tubing adapter —
1/8-inch NPT x ¼-inch (or 3/16-inch) barb
|15||Supreme Mag2 pump||AE||MD2||1||$37.90|
|16||½-inch PVC 90 street ell
(MNPT x Slip)
|17||½-inch PVC female adapter
(Slip x FNPT)
|18||Nipple ½-inch MNPT x ¼-inch MNPT||AE||62083||1||51¢|
|19||½-inch MNPT x ½-inch barb||AE||62018||1||46¢|
|20||½-inch PVC pipe||LH||3 feet|
|* = Female
National Pipe Thread|
** = Male National Pipe Thread
|½ Pint PVC and CPVC Clear Primer||ALS||P-6866C-H||$3.20|
|½ Pine PVC Solvent Cement||ALS||700-H||$3.85|
|1 Pint WELD-ON 1802||AIN||$5.60|
|Teflon Tape — ½ inch x 260||ALS||S260||79¢|
|Marine Goop or Plumber’s Goop||LH||$5.50|
|SOURCES FOR PARTS|
|Company||Phone Number||Web Address|
|Aquatic Eco-Systems||(800) 422-3939||http://www.aquatic-eco.com/|
|ALSCO Industrial Products, Inc.||(800) 849-3030||http://www.alscoind.com/|
|US Plastics Corp.||(800) 537-9724|
|AIN Plastics, Inc.||(800) 431-2451|
For the body of the reactor, you can use either 4-inch PVC pipe, 4-inch clear PVC or the 4½-inch OD acrylic tube. I prefer to use the 4½-inch OD acrylic tube because it works well with 4-inch PVC fittings, and if you like to see into the reactor, then it is economically a better choice to use than the 4-inch clear PVC, which tends to be more expensive. Unfortunately, it is not easy to get a 2-foot piece of the acrylic tube via mail order, as most places will only sell it in 5-foot increments, or have a minimum order that will not be met with the purchase of just this piece. The best source I have found for precut pieces of acrylic tubing in sizes that work with PVC fittings is Aquatic Eco-Systems, Inc.
To assemble the threaded fittings to the reactor body I prefer to cut pipe taps rather than just gluing the fitting into a hole. Drilling the appropriate-size hole and gluing the fittings is perfectly fine if you don’t want to make the investment in pipe taps. For those of you interested in making National Pipe Tap (NPT) threads, the following information may be of interest. The ½-inch NPT can be made by first drilling a 23/32-inch hole and then using a ½-inch NPT tap. Attaching the fitting with the threads will allow for easy disassembly of the recirculation loop (in case you need to use the chamber for other purposes or redo your design).
Pipe taps can be purchased from MSC Industrial Supply Company. I find it very handy to have 1/8-inch, ¼-inch and ½-inch NPT taps, and corresponding drills. The table below provides the information of the drill, taps, and part numbers from the MSC Industrial Supply Catalog.
|1/8 inch||04350021||$3.17||11/32 inches||01180223||$1.27|
|¼ inch||04350039||$3.58||7/16 inches||01180280||$1.97|
|½ inch||04350054||$6.73||23/32 inches||01340462||$7.99|
|¾ inch||04350070||$10.67||15/16 inches||01340603||$11.10|
To glue the acrylic to PVC ideally you will need an adhesive that is designed to glue acrylic to PVC (e.g., Weld On #1802 (or Weld ON #40). These can be bought from AIN Plastics. Although, I have used regular general-purpose PVC cement and it has held well so far.
For those of you who would like to know more about working with plastic threaded fittings and making leak-proof fittings, Lasco Fluid Distribution products provides excellent information, including “How to Avoid Problems with Threaded Plastic Fittings”. To learn about working with plastic solvent cement you can read “Solvent Cementing Procedure” — it’s in a nice enjoyable cartoon format. Another good article on the same site is “Leak-free PVC Joints”. A tube of Marine Goop will come in very handy in sealing the joints from the inside of the reactor to prevent any leaks caused by sloppy gluing.
Assembly Steps (Refer to the “Materials Lists” above for the parts numbers listed here in parentheses)
Step 1 — Building the mixing chamber.
Step 3 — Support for the media.
2) Recirculation Loop
This is the part of the construction that will take the water in the mixing chamber and keep it recirculating through the medium. The basic recirculation loop used here is a reverse flow through the media. I like this for several reasons — it keeps the media from compacting and, because the particles tend to stay loose, it prevents channeling. The downside is that the intake to the pump can run dry if the water level drops inside the reactor to the point where it cannot be pushed through the loop. You can easily modify the design to run in a top-down flow scheme, if this becomes a big concern, simply by changing the way the pump is mounted.
The basic construction here is very easy and similar to any plumbing you may have done in setting up your tank and is shown in Figure4. The unions will help in assembly of the reactor and in taking it apart for cleaning the pump and when adding media. I have raised the pump so that the complete assembly takes up a smaller footprint.
3) Input and Output from Tank
The water enters the recirculating loop via a needle valve (13). The needle valve is needed because most reactors are only operating at 20 to 50 milliliters per minute and this adjustment is difficult to make with a ball or gate valve. A small powerhead is used to pump water from the sump into the reactor through the needle valve.
The output (12) is a tubing adapter — elbow ½-inch NPT x ¼-inch hose barb — fitting placed at the highest point of the recirculating loop. The output basically is the overflow from the reactor. The amount of output will depend on the rate of input. I initially had the needle valve at the output, but it tended to clog easily due the calcium deposits formed by the effluent running through the needle valve. The reason for restricting the barb fitting to a smaller size was to make it difficult for the CO2 to escape from the reactor.
Important Note — When attaching the powerhead to the input port via tubing, make sure you use a check valve to prevent water from the reactor draining back into the sump when the reactor is shut down for maintenance. Also, this check valve will prevent water from the reactor draining out in case of a power failure or failure of the powerhead. If the powerhead fails and water drains out, it will cause the re-circulation pump to run dry and burn out. The Polypropylene Check Valve (Part # 228215 from Aquatic Eco -Systems; $2.95) works well, as it is designed to work with different-size tubing and does not have to be in a fixed orientation to work.
4) CO2 Injection System
CO2is introduced into the reactor through a 1/8-inch NPT x 3/16-inch hose barb fitting (14). The fitting is attached to the 90-degree elbow by drilling and tapping a 1/8-inch NPT into the elbow. Once again, this can also be glued in place instead. The CO2 input is placed so that the CO2 bubble can easily enter the pump and be broken up by the impeller into smaller pieces to facilitate mixing of the CO2 and the water.
Regulators come in either a single gauge or dual gauge model. In the single gauge model, the gauge provides the reading for the output pressure only. The dual gauge regulators provide an additional gauge that shows the pressure inside the tank. This helps in monitoring when the CO2 is running out, although with CO2, pressure remains fairly constant throughout. Once it starts dropping it drops very rapidly, so the gauge for monitoring CO2 tank pressure can be eliminated. Regulators can also be purchased from the same sources as the CO2 tanks. My regulator is currently set at 20 to 25 psi.
The names of the dealers for the ARO valves in your area can be obtained from ARO Corp. (419-636-4242). Grainger also carries these valves: 1) ARO model FO1, NPT size 1/8 inch, Grainger Stock No. 6ZC07 and 2) ARO model F02, NPT size ¼ inch, Grainger Stock No. 6ZC08.
I am currently using the Whitey Model no. B-ORF2 valve (around $25). I was able to purchase it from the Pittsburgh Valve and Fitting Company (P.O. Box 4155, 49 Meade Ave., Bellevue, Pittsburgh, PA 15202; 412-761-3212 or FAX 412-761-2486).
Another valve that I have not tried, but that has been recommended, is the slightly more expensive Nupro B-4MG2 valve. This valve can also be obtained from the company listed above. If you have trouble finding these valves contact a Swagelock dealer in your region. Swagelock is the parent company for Nupro and Whitey.
Modification Notes — A flow control valve can in fact replace the CO2 needle valve and bubble counter and is cheaper than the two items combined. This valve not only provides the visual feedback, but also provides a reading on how much CO2 is being injected in a more quantitative form (e.g., cubic centimeters per minute; cc/min). The flow control valve I am using is the Dwyer RMA-151-SSV Flowmeter, range 5 to 50 cc/min air with stainless steel valve. I find I am using about 20 cc/min of CO2.
After filling, make sure the threads are clear of any media particles. Using Teflon tape to coat the threads on the male end, tighten the cap, using a large wrench, by grasping the square projection on the cap. Make sure you tighten enough so you don’t get a leak. I personally found it difficult to get a good seal on the 4-inch threads with the Teflon tape and have now switched to using Teflon Pipe Dope, available from ALS in a ½-pint size (part # TF8, $7.38). This is a soft setting compound that seals pretty well and also allows the threads to be taken apart for refilling. It does seem nasty at first, but I have used it without even letting it dry and it has not affected the tank in any visible way.
To get the reactor started, first open up the needle valve controlling the water input and start up the powerhead to fill the reactor completely with water. Give the reactor a few shakes to drive the entrapped air out of the media. Let the water fill up the complete mixing chamber and the recirculation pipes. Letting the water run for a while, you will get a steady stream of water from the output. Now start up the recirculation pump. You might see that the media lifts and separates into two regions —don’t worry about it, it will not affect the operation of the reactor. As the media is stirred, some more entrapped air will be released. Now cut back the flow of the input water via the needle valve to a steady drip. Turn on the CO2 until you get about 10 to 15 bubbles per minute.
There are basically two adjustments that can be made to an operational reactor — the effluent flow rate and the amount of CO2 added. In the steady state, the trick is to balance the output of the reactor with the daily consumption of alkalinity in the tank.
Increasing the CO2, while maintaining the effluent flow rate, results in a decrease in the pH of the reactor and hence an increase in the solubility of the CaCO3 media, and hence a higher alkalinity in the effluent. This increase in alkalinity of the effluent will be seen up to a pH range of 6.3 to 6.5 and any further decrease of the pH in the reactor will start resulting in decreasing alkalinity. Increasing the effluent flow rate, while maintaining a fixed amount of CO2 will result in an increase in pH in the reactor and hence a reduction in the alkalinity of the effluent. By adjusting both the effluent flow rate and the CO2 injection rate, a fixed pH can also be maintained in the effluent. Some advocate maintaining a fixed pH of around 6.5 in the reactor.
I find it much easier to adjust the reactor based on the alkalinity output rather than the pH measurement. I would recommend first setting up an effluent flow rate so it flows in a continuous steady drip, and then making adjustments to the CO2 flow rate to increase or decrease the alkalinity of the output. For most tanks this approach will work fine, but if you have a heavily loaded small-polyped scleractinian (SPS) coral tank, then it may require you to increase both the effluent flow rate and the CO2 injection rate. A certain amount of fine-tuning is required to adjust the reactor for your particular system.
Having a good estimate of the daily consumption of the alkalinity in the tank and understanding some of the “reactor math” can help in eliminating some of the trial and error in fine-tuning the reactor. Let us assume that the reef system contains T liters of water, and the effluent flow rate is L liters per hour and the estimated daily alkalinity consumption is c milliequivalents per liter (mEq/L) per day. Now, measure the alkalinity in the tank and the alkalinity of the effluent. The difference between the two values will give you the increase in alkalinity due to the reactor — call this d (mEq/L) — as follows:
alk/day added due to the reactor = (d x L x 24)/T Equation 1
So, now we need to adjust the reactor so that the daily increase due to the reactor is approximately c mEq/L. This will give us the setting at which the reactor will replenish the alkalinity that is consumed daily.
Looking at the Equation 1, we can see that there are three ways this
can be achieved:
Only adjusting d — the increase in effluent alkalinity
Only adjusting L — effluent flow rate
Adjusting both d and L.
The effluent alkalinity can be increased (or decreased) by correspondingly increasing (or decreasing) the amount of CO2 and keeping the effluent flow rate constant. This provides one convenient way of tuning the reactor output to the aquarium needs. When increasing the amount of CO2 added care must be taken to keep the pH level above approximately 6.3. I personally use this approach to adjust my reactor. If I find that I have to injected too much CO2 so as to cause the pH in the reactor to drop below 6.3, I am better off also increasing the effluent flow rate through the reactor.
Increasing the flow rate will result in a decrease in effluent alkalinity if the CO2 flow rate is not simultaneously increased. Several manufacturers recommend adjusting both the flow rate and the amount of CO2 simultaneously to maintain a constant pH (about 6.5) in the reactor and hence a constant alkalinity output in the effluent. I prefer having to just adjust one parameter — the CO2 flow rate. Both approaches will satisfy the needs of the user, but the key is to balance the daily consumption to the daily addition of alkalinity.
Overall, the use of a calcium reactor has moved me another step closer toward the ultimate goal of becoming the lazy aquarist who spends time enjoying the tank, rather than working on the maintenance chores — other than trimming my fast-growing SPS corals, of course. If you have any further improvements you would like to suggest or have any comments about the article, please feel free to contact me at firstname.lastname@example.org
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