A recirculating calcium reactorby Chris Paris for Reef Aquarium Information Depot
A bubble counter.
CO2 enters through the top connection. The white object is a check valve. The gas is released into the bubble counter at the bottom of the rigid airline tubing that appears in the center of the main tube.
Water from the aquarium is pumped into the bottom connection by a small powerhead located in the sump of the reef setup.
Some of the CO2 dissolves in the water within the bubble counter, and some leaves it still in gas form. A combined CO2/water product leaves the bubble counter through the side wall of the tube.
From there, it goes through the plastic needle valve, which is used to control the rate at which the aquarium water passes through the calcium reactor. Premixing the CO2 and aquarium water lowers the pH of the mixture to about 5.8, and ensures that calcium carbonate is highly soluble in the fluid that passes through the valve. That keeps the valve from clogging with calcium deposits.
After water comes out of the righthand side of the needle
valve, it will be taken via flexible tubing to the input of
the calcium reactor.
This is the calcium reactor itself. The main body of the reactor is an acrylic tube that I acquired from a surplus supplier. It is 9" on the outside, 8.25" on the inside (yes that's right, 3/8" wall), and 10" tall, not including the sheet material that makes up the bottom and the top. The tube dates from the early 1960s, and perhaps because of this age, it suffered more "crazing" (small hairline cracks) during the gluing operations than most of my other acrylic work. It still holds water!
A CO2/water mixture enters the reactor through a hose barb connection on the lid. This low pH mixture is quickly recirculated within the reactor by the internal circulation pump (a Maxijet 1000). The circulation is from the top of the reactor to the bottom, through an acrylic tube running down the center of the reactor. Water of high calcium concentration and alkalinity exits the reactor through an exit on the lid.
From above, we can see the input and output features of the reactor. The CO2/water input mixture enters the reactor through the black hose barb. This dumps the input directly over the intake to the circulation pump, so that the first thing that happens is that the mixture is pushed down to the bottom of the reactor. I don't think that this placement of the input is critical in this reactor design, but people are used to it.
Water can exit the reactor through two paths. One path is through the lid, and then through a small ball valve on the lid. When the ball valve is open, liquid or gas can exit the reactor through this path. The fluid is drawn from the very top of the reactor, so either water or gas can exit through this path. The second path for fluid to exit is up through the lid, and then through the white nylon tee. This exit path has a 1/2" tube glued to the inside of the lid, under the hole through the lid, so that fluid is drawn from half an inch below the top of the reactor. This ensures that only liquid will exit the reactor through this path. Undissovled CO2 will be trapped at the top of the reactor.
When the user just closes the reactor, it will have air at the
top. By operating the reactor with the valve open, this air
will be allowed to escape. Then the user may close the valve,
which ensures that any additional gas, which will be CO2, will
be trapped within the reactor until it reacts. This ensures
efficient use of CO2.
This is the joint between the acrylic tube in the center of
the reactor and the bottom of the reactor. This tube carries
the output of the pump down to the bottom of the reactor. The
bottom of the tube contains four slots in it, each 1/4" wide
by 3/4" tall. The water exits the tube through these slots. It
then moves up through the aragonite that will be in the
reactor, and returns to the pump intake at the top of the
Here we can see the circulation pump and its associated plumbing. The intake side of the pump is connected to a 1/2" CPVC "street elbow" and a short length of 1/2" CPVC pipe, so that the pump draws from near the top of the reactor, and also right below the mixed CO2/water input to the reactor.
The output of the pump is a slip fit into a 1/2" inside diameter acrylic tube. This tube carries the flow from the circulation pump down to the bottom of the reactor.
The power cord to the pump goes through the lid of the reactor. To achieve this, I drilled a 1/4" hole for the cord, cut the plug off, threaded the cord through the hole, spliced the plug back on, and sealed the gap between the cord and the hole in the lid.
On the left side of the image, just left of the circulation
pump, you can see a 1/2" length of acrylic tubing glued to the
lid of the reactor. This short tube surrounds the hole in the
lid that leads to the white nylon tee on the lid of the
reactor. Water exits the reactor from this point. The short
tube on the inside ensures that what leaves the reactor is
liquid, not CO2 that hasn't had a chance to react yet.
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