Acrylic and PVC Style

By John J. Geisler

There are a number of different versions of "Do-It-Yourself" PVC style Kalkwasser reactors available on the internet and most of them are pretty similar with a few variations.  Detailed below is the process I used for fabricating my reactor, some information on the parts and the results I had (some good, some not),  I hope this helps with any other individuals attempts to construct their own reactor.

Along with the description and photos listed below I have included a set of printable CAD drawing and parts list saved as a PDF file (Adobe Acrobat).  Click on the picture of the Kalkwasser reactor to the right to open the file. These drawings can then be printed to provide dimensions and detailed drawings for use during construction.

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Top Cap:  4" schedule 40 PVC Female adapter Socket x FPT
The piece to the right is the 4" male plug, schedule 40 PVC. Used for the top section of the reactor.
Source:  Home Depot

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Main coupler socket:   4" schedule 40 PVC, Socket x Socket.
This is the main center portion of the body of the reactor, the top and bottom tube sleeve into this section.
Source:  Home Depot

coupler.jpg (49345 bytes)

Bottom Cap:  Schedule 40 PVC 4"Cap - socket
There are several things to look for with this piece.  Some manufacturers have a completely smooth inside for the cap.  This brand had a raised disk in the very center.  Some people have reported that the raised disk button helps to distribute the water flow while mixing but I can not substantiate this claim although I did choose a cap with this button.  You will need to cut this cap down in size (recommended but not critical) by trimming 1" off the top edge, more later.

Source:  Home Depot

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Bottom Base:  4" Toilet Flange, PVC Schedule 40.
This pieces will mount to the bottom cap when the reactor is completely assembled.  To aid with the fit a used a router with a 45 degree bit and trimmed the inside edge to help fit the curved cap.
Source:  Home Depot

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Main Body:  4 1/2" Clear Acrylic, 36" long.
This one is the tough part, the 4 1/2" clear acrylic main body for the reactor.  Most plastic and acrylic suppliers will only sell in minimum of 6' length or charge a substantial premium for the cut piece.  Listed below is one source that will sell the piece by the foot at a very reasonable price.  The main body is 4 1/2" OD clear acrylic 36" long.  This will later be cut into two section 12" & 24". When purchasing I recommend ordering the 36" piece already cut at 12" and 24". Without a 15" power miterbox this is not an easy piece to cut.

Source:  Aquatic Eco Systems


Mixing Motor:  RIO 50.
This is one area that really varies in personal preference.  The picture to the right is the modified RIO used.  I used a 90 degree 3/8" Socket x FPT elbow and had to ream out the slip opening to fit the intake on the motor.  I then glued the elbow onto the motor.  I also glued the valve that comes with the motor onto the out-put part to create the motor in the picture with the addition of a threaded hose barb in the elbow.
Premium Aquatics
Marine Depot

rio50_motor.jpg (46718 bytes)

Various hose barbs:
(1) Thread to barb adapter-Elbow 1/4" NPT x 1/4" hose
(3) Thread to barb adapter-Straight 3/8" NPT x 1/2" hose
(1) Thread to barb adapter-Straight 3/8" NPT x 1/4" hose
Source:  Home Depot
Source:  Us Plastics
Aquatic Eco Systems

Picture of hose barbs and details pending

Couplers and Adapters: PVC Schedule 40 gray
(2) Female adapter - straight socket x FPT 3/8"
(2) Elbow 90 degree socket x FPT 3/8" (one is for the pump)
(2) Elbow 90 degree socket x socket 3/8"
3/8" ID clear PVC tubing, approximately 24", various sizes

Note: If 3/8" tubing and parts are not available, 1/2" ID PVC tubing (white or clear) can be substituted, adjust couplers and parts accordingly. The RIO pump does need a 3/8" elbow.
Source:  Home Depot
Source:  Us Plastics
Aquatic Eco Systems

tubing.jpg (42252 bytes)

Tubing Quick Connects:  Colder Products Company.
These things are great!  The manufacturer Colder Products is a local Twin Cities, MN company which is how I first discovered the parts.  They originally where only available to manufactures but recently they are now being carried by other plumbing supply companies  What is needed is the PLC Series Hose barb Coupling Bodies and Coupling Inserts to make a pair.  The important thing to get the ones with the auto shutoff valve in each coupler.  When the water lines are disconnected, the water instantly stops, no drips!

Source:  Us Plastics

quick_conects.jpg (87401 bytes)





The first step in the assembly process is to cut the 4 1/2" acrylic tube to size.  I cut the bottom section at 8" leaving 16" for the top section.  This is not a critical dimension, just a reference.  If you have a radial arm saw or 15" chop box great....if not you'll need to set up a jig to provide a clean straight cut for these pieces...This is very important.  File or sand the cut edges to remove any burs, inside and out.

After cutting the main tube, test fit the pieces to the center coupler.  Slide the pieces all the way together.  Now wrap tape around the tube to mark the end of exposed part of the tube.  This serves several purposes.  It provides a positive stop mark when sanding the tube and protects the tube from glue and "gunk" during assembly.  

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Note: In the photos above and subsequent photos, I used a "V" block during assembly.  Click here for instructions on making a V-block.




Before assembling the bottom cap you will need to cut the cap to size.  The cap originally has a 2' lip for the slip connection.  This is deeper than necessary for the reactor and hides the bottom mixing area. It is recommended to cut approximately 1" off the cap.  To cut the cap I used a table saw and rolled the flat part of the  cap around against the fence to cut approximately 7/8" off  (1" with blade thickness)  What you use  obviously dependent upon tools available.

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Repeat the dry test fit and wrapping with masking tape for the top and bottom cap also.  Be sure and sand the end of the tube completely and the inside of the PVC connectors.

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This is the supply mixing tube.  You'll need to take some careful measurements when fitting this tube.  This is the piece that projects from the middle of the reactor body and connects to the mixing motor.  When fitting the main tube that projects inside the reactor body fit the tube so it is positioned directly above the center button of the bottom cap leaving approximately 1/4" clearance. (Note:  The piece on the end is dry fitted for the picture only, this is glued on later.)

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Before assembling this part, sand and prep the elbow and ends of the tubing. Clean and bevel the bottom end of the supply tube also.


The output flow connection is similar to above.  It is mounted above the supply connection similar to above.  I used a piece of 3/8" clear PVC tube to create the 1 1/4" stub that projects through the coupler and into the reactor body. This is a straight piece only and does not have an elbow return.


This is the 3/8" female adapter, socket by FPT, threaded connector that gets installed on the ends of the supply mixing tube and output tube. A very good method of coping these connections to fit the side of the tube is to wrap a piece of 80# or 100# sand paper around the tube to be fit and then tape in place. Run the connector the length of the tube until the connector had a complete coped end. Remember, only cope the socket end, not the treaded end.

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After dry test fitting and sanding all the pieces, when gluing the components for final assembly there are several procedures to make sure you follow:
1st: Wipe all the surfaces with the cleaner.
2nd:  Wipe all the surfaces with the primer, allow this to set for one to two minutes as it softens the plastic for better bonding.
3rd:  Coat both surfaces to be bonded with the PVC cement.  Once the pieces are slipped into place for gluing, make sure they don't MOVE.

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This glue was used for several of the odd shaped pieces that the regular PVC cement wouldn't work for.  It seemed to work fine for most of the plastics but didn't seem to work as well for bonding PVC to PVC.  I originally used it to bond the base plate to the round bottom cap and these pieces later popped apart.  This lead to another whole story we won't cover here.......

For gluing the PVC couplers and tubing to the main body I recommend Weldon 40 two-part adhesive. A little more difficult to work with than the ready made products but a VERY strong bond.

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The first actual pieces of the reactor body to be glued together are the top and bottom cylinders and the main body connecting sleeve.  Follow the steps listed above for gluing. 

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After the coupler and the top and bottom cylinder are glued and set you can drill the holes for the supply and out-put tubes.  This was a slight challenge to drill a hole that matched the 3/8" ID acrylic tube as the OD was an odd size, .675".  Greater than 5/8" less than 3/4".

To achieve this odd size I took a 3/4" paddle bit and ground down each side equally until I had the proper size to match the tubing OD.  There aren't many drill bits easily available in the larger sizes in the 64th increments so this becomes another project in itself.

Another option for the drill bit is a Bi-metal hole saw. These are one of the few bits I've encountered that come in an 11/16" and 13/16" size.

I drilled a 1/8" pilot hole through the pieces first help guide the larger drill bit.

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If using the RIO50 pump, drill the two pump holes 1 1/2" apart, 3/4" on each side of the center divider of the connector.

At this time rotate approximately 45 degrees and drill a 1/2" diameter hole approximately 1" down from the top edge of the connector. This is for the RO water intake barb.  Tap this hole to fit a 1/4" NPT barb.

1-4_NPT_tap.jpg (46257 bytes) 

Test fit the supply mixing tube and parts before actually bonding the parts. Double check the tube length also.


Bond the top intake connector first. This the piece with the 1/2" long stub sticking out of the straight threaded adapter. After bonding the 1 1/4" tube into the connector piece, apply a bead of adhesive around the intersection of the PVC tube and the connector piece. Insert the assembled piece into the top hole and seat the coped face to the side of the reactor body.


I use duct tape to hold the parts in place during bonding. Place the tape on the center of the piece first and then stretch both tape sides equally.

connecter_duct-tape.jpg (21421 bytes)

This helps show the tube and connector after it has been glued in place. Glue the top connector with the 1 1/4" stub in place first. The is the connector for the pump return.

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In this step I've inserted the supply mixing tube inside the lower tube and then through the hole into the main body of the reactor.  I stuffed rags into the cylinder to keep any excess glue from dripping on the cylinder and help hold the tube in place while the glue sets.  You need to complete this step before the bottom cap in glued in place. 

Once the end of the short tube is inserted through the reactor body hole, apply a bead of adhesive around the edge of the hold and the tube. Now coat the inside of the connector pieces with adhesive and the coped face of the connector. Use plenty of glue around the opening where the tube comes through the coupler body.  This is an area subject to leaks so take care now.

Insert the connector piece on the end of the tube, seat the coped face to the reactor body and tape in place. 

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Once the adhesive has set and the tubes are secure enough to move, remove the rags and turn the reactor so the connectors are facing straight down. Using a wood applicator stick, stir stick or similar, reach inside the reactor body and apply a bead of adhesive around the inside edge of the PVC tube where it passes through the realtor body. Let gravity fill the adhesive around the tube opening. While a little more work, this is the guarantee for the connection. I have never had a leak or loose connection using this method.


Another photo with both tubes glued in place.

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Another photo of the intake and output tubes in place as seen from the inside.

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Once the supply mixing tube and the output tube are glued in place you can glue the bottom cap in place. Do not glue the end cap on until all the internal connections are finished as you won't be able to go back in and work on these.

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Once the end cap is glued in place you can attach the base flange. As noted previously I recommend routing a 45 degree chamfer around the top edge of the base for a better fit.

Stand the reactor upside down so the end cap is on top. Mount the reactor so it does not fall over. Acrylic is not very durable and if the reactor tips over……you get to start over. If you have an extra base flange of don’t mind investing a few extra dollars, use an extra flange to hold the reactor while working on it. Anchor this flange if you do.

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Sand the perimeter edge of the end cap where it will contact with the base flange. Clean and prep both pieces. You can use PVC cement to bond the two pieces, if you have Weldon 40, even better yet. You can apply an extra bead on Weldon 40 around the inside edge for maximum strength.

Once you position the flange on the end cap during bonding, make sure it is perfectly straight. If the flange is not STRAIGHT you will have the leaning tower of Kalkwasser. I used some making tape to hold the flange in place during bonding once it was positioned.
Note: In this photo it shows the RO intake in the base. In the current design I have moved the intake to the middle collar section.

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 I believe the top section is the part of this design that is slightly lacking. The top cap is very tough to get to seal and usually requires a LOT of Teflon tape.

For my first reactor to form a better seal, I created an internal gasket inside the top, just below the top cap plug. To create this gasket I first coated the bottom edge and about the first turn of thread on the top cap plug with petroleum jelly. I then screwed the top cap into the main top and lightly hand tightened. From the bottom, inside the cap I applied a heavy bead of silicone around the perimeter of the junction of the plug and the cap body. I used my finger to smear a smooth gasket around the body of the cap.

Once the silicone was completely cured I carefully unscrewed the top cap plug leaving the silicon gasket inside the main cap. Be sure and wipe out the petroleum jelly and completely clean before assembly.

With this reactor I did not have a problem with leakage around the top cap plug. This reactor had a slight accident (acrylic doesn't do falls well) and I had to build another one. I did not make a gasket in the second unit and I have had a problem with a slight leakage around the top cap plug. Lots of Teflon tape…..

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Once the gasket part is completed and the top is completely clean the top can be bonded to the top acrylic tube section. Repeat the sand, clean and prep procedure and PVC bond the top to the tube.

Once the cap is bonded to the reactor body drill the 11/16" (or 13/16" for 1/2" tubing) for the effluent assembly. (Refer to the PDF file drawings for location and details)

Take the top cap plug and drill a 1/2" hole in the center of the 2" square area on the top of the plug. This will be the highest point in the reactor when assembled. Tap 1/4 NPT threads in the hole once drilled. Install the chrome air valve in the top of the plug cap. Be sure and seal the valve when installing, I typically use clear silicone or plumbers goop on the threads of these little valves.

 chrome_valve1.jpg (34740 bytes)

Note: I do not recommend these little plastic valves shown to the right. I have used these on several projects and every single one has failed. I have since removed these valves and replace them with the small chrome ones.

 sampling_valve.jpg (44580 bytes)

The top effluent assembly is very similar to the mixer assembly but the down tube is only about 1 1/4" long. Repeat the assembly and installation procedure similar to the mixing tube assembly listed above.

For the external connector install the 90 degree elbow (Soc x FPT). Cope the socket side similar to above so the elbow points straight up. You can later install either a hose barb of a quick connect fitting in this connector. I recommend the quick connect.




The pump is one of the many areas that can vary as part of the design for this reactor. Some people have used a Maxijet 250 for the pump but I have heard of leaks with this pump. I used a RIO 50 and modified the pump slightly.

Take the 3/8" gray PVC elbow and bore the socket opening oversize slightly using the 11/16" bit or Dremel so it fits over the nub on the intake side of the motor. Once fit properly, PVC bond the elbow to the pump so you get a good seal. You might want to install the hose barb in the elbow piece before bonding to the pump to prevent the chance of damaging the pump or connection during the barb installation.

Take the variable flow valve that comes with the pump and bond this part to the output side of the pump similar to photo.

 Measure and cut two pieces of 1/2" vinyl tubing so the tubing is 1" longer than the end of the flow valve end when installed. The piece of tubing for the upper barb on the intake side will be slightly longer but the ends should be equal once both are installed. Clamp the hoses to the pump.

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Install one 3/8" NPT x 1/2" hose barb in the end of each of the connectors on the reactor

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 Install the hose ends on the pump onto the hose barbs on the reactor. Clamp the hose connections.

Note: When installing vinyl tubing onto hose barbs it is often helpful to use a hair dryer to heat the ends of the tubing during installation. This softens and stretches the tubing making it easier to slip on and the tubing shrinks back when cool for a tight fit.

motor_assembled.jpg (34120 bytes)



The purpose of this reactor is to take a constant supply of RO water, mix it with calcium hydroxide (kalk) to create a Kalkwasser (chalkwater) solution. This solution is then pumped out and dosed to the reef system, either in the main tank or typically in the sump.

My recommendation is to use an elevated RO holding tank to provide the constant water supply. By elevating the tank, the weight of the water and gravity creates line pressure. Same principle as a water tower. More details on this elsewhere in the DIY section.

 drip_system_04.jpg (44197 bytes)

For the RO water intake you can either connect the 1/4" vinyl tubing directly from the tank to the reactor or use a quick connect. I used CPR PLR series inline barb, quick connect for my supply and output lines. This allows quickly disconnecting the line and stopping the water flow in the case of maintenance or cleaning.

 quick_connect-02.jpg (23982 bytes)

Mount one end of the vinyl tubing onto the end of the hose barb located at the middle section of the reactor. This is the RO water intake. If using a quick connect, install a male insert in the other end of tubing about equals to the top of the reactor. If not using a quick connect this can be attached directly to the RO tank (not recommended without using some sort of shut-off valve).

At the top of the reactor, you can either install a quick connect female coupler body into the top of the elbow or install a 1/4" hose barb. This is the Kalkwasser effluent output connection.

From this output you will be connecting the reactor to the dosing pump of choice.

Note: do not try and use the converted hospital style peristaltic pumps for a Kalkwasser dosing pump. I have tried and not had good results for a variety of reasons.




Now that your reactor is assembled time to test it for leaks. If you did everything just right you won't have any but you still want to test it first. Fill the unit with tap water (don't waste RO) make sure the input and output lines are closed and plug the unit in.

To get a true test you will need to hook up a water supply to the RO intake line and close the reactor tight. Open the air bleeder valve and let the reactor fill until a bit of water comes out the air valve. Close the valve and your reactor system is now filled and air tight.

Let it run for a while and make sure the system can run under pressure without any leaks. Watch the seal around the plug cap and the main top cap. If any leaks, apply Teflon tape around the plug.


Once the reactor has passed the leak test time to put it to work. Time to install the unit for operation. Open the reactor and dump the tap water, final inspect and clean.

Pick a location where the unit is accessible but will not be bumped and damaged. Make sure to bolt the unit down to a stable base that will not allow the reactor to tip over.

Connect the reactor to the RO supply and let the reactor start to fill with RO water.

reactor-utility_rm.jpg (36098 bytes) 

If your reactor is the 36" version, this reactor has a capacity of approximately 540 cubic inches which equals 2.34 gallons of water.

Once the reactor is to within a couple of inches of the very top add the Kalk powder. I typically use five heaping scoops (the ones in the container) per filling. Let this mix with the water and drop from the surface so you no longer have a pile setting on top of the water. Open the air valve on the top plug and tightly install the top plug on the reactor.

kalkwasser_powder.jpg (47450 bytes)

The top plugs can be a little awkward to tighten without damage to I made my own custom cap wrench for tightening the top plug. This thing works great!

 cap_wrench.jpg (47536 bytes)

Once the top plug is in place and tight, start the RO water flow again. Let the reactor fill until water appears out the air valve.


Now that your reactor is loaded and ready to go, it needs to mix. For this I highly recommend the Intermatic digital timer DT 17. This timer can be programmed to start and stop fourteen times per 24 hour period for as little as one minute. I have mine programmed to run for approximately four minutes every ninety-eight minutes.

Before starting to dose Kalkwasser from your reactor I recommend you let it cycle for twelve to twenty-four hours first. This allows the Kalk to create a mixture and for the initial filling to settle down so you're not dosing any of the kalk powder into your main system.


Congratulation….you're ready to start dosing Kalkwasser!


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