How to Build Your Own Aquarium Chiller

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Updated on 05/10/22

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Marine aquarium with fish and coral — Credit:
WolfmanSF / Wikimedia Commons / CC BY-SA 4.0)

Total Time: 2 hrs
Skill Level: Intermediate

Some reef aquariums require water temperatures cooler than typical room temperature. Having water from the aquarium sump or filter pumped into a chiller, then returned to the aquarium can bring the water down to the desired temperature. You can make your own aquarium chiller with these plans from Don Carner. This is a quick and inexpensive method for maintaining a steady aquarium temperature, especially during those long hot summer months.

Cost Considerations

These are estimates for how much you will spend on the project:

The refrigerator should cost $89 to $199 depending on the size you choose.
The Rio 2500 runs about $80-100 at your local fish store.
The fittings, tubing, and pipe shouldn't run more than $10 to $15, depending on how much and what style you choose.
Hopefully, you already have a drill and the bits.

A reasonable estimate is $200 once completed, which is still significantly cheaper than a commercial unit ($400 and up). While not as efficient as commercial chillers, this is a viable alternative and will decrease your water temperature surprisingly well. Use a pre-set or variable heater to balance the temperature within the sump and it'll become hands-free.

Emergency Chiller

If you just need a temporary emergency chiller to help keep your tank temperatures down for a few days, substitute an ice chest (even one of those inexpensive styrofoam ones will do) for the dorm-sized refrigerator and fill it with ice. Drop the tubing coil in it and you are ready to start chilling.

Chiller Diagram and Instructions

The diagram shows these elements:

A: Water coming in from the aquarium sump
B: Chilled water returns to the sump
C: Freezer compartment with a temperature probe attached to the inside wall of the cooling box
D: 3/8-inch coiled plastic tubing
E: The refrigerator housing and inner plastic box

What You'll Need

Equipment / Tools

Hand drill and 1/2 inch drill bit
Screwdrivers
Pump or powerhead

Materials

Dorm-sized refrigerator
50 to 100 feet of 3/8 inch plastic tubing
PVC fittings (90-degree elbows or straight connects, threaded or slip)
Aquarium-safe silicone sealant
1/2 inch thin-wall PVC pipe

Instructions

If possible, remove the metal box that isolates the ice cube tray/freezer section, but leave the temp probe alone. This will give a better overall temperature control within the cooling box.

The more coils, the better the temperature-reducing effect and the more efficient the unit operates. Depending on the brand/model of the refrigerator that you are using, you may encounter insulation between the housing and the inner box when drilling your input/output holes. There is no need to seal the refrigerator door. You might need access if something goes wrong down the road. Besides, it's a great place to keep your additives that require refrigeration after opening them.

Drill Access Holes

Drill your access holes in the top or sides, it doesn't matter.
Cut PVC Pipe

Cut two pieces of the PVC pipe about 4 inches each.
Insert Pipe

Insert through the holes drilled and seal very well with the silicone.
Reinforce Pipes

You may want to reinforce these pipes with a little five-minute epoxy before sealing them with the silicone. This keeps them from sliding back and forth and breaking the cured silicone seal should you want to move the fridge down the road.
Glue Fittings

Glue or thread your fittings onto these two access pipes. You can use nylon threaded nipples to connect the 3/8 inch tubing coils inside the cooling box. Outside, you can glue slip fittings reduced to accommodate the tubing running from the Rio 2500 sump pump to the chiller and back to the sump.

That's all there is to it. Remember that the more coils inside the refrigerator, the better your cooling effect will be.

Using the Chiller

Set the chiller as close to the sump or aquarium cabinet as possible. The further the run of plastic tubing from your sump to the chiller and back, the greater the temperature change due to ambient room temperature. You could use pipe insulation wrapped around the tubes, but this is rather unsightly and not necessary unless living in a very hot environment.

The operation is straightforward. Remember to keep the flow fast enough to prevent freezing of the water in the coils inside the box. If equipped with a thermostat, your fridge/chiller will be easier to control. Some models only allow you to set the main box temperature, not the freezer compartment. That's another reason for removing the aluminum ice cube divider and tray. The probe that is attached to the wall of the freezer area will now monitor the entire cavity. Set the refrigerator thermostat to the level that maintains the chilled water at the appropriate temperature to keep the aquarium temperature constant.

Try to use opaque tubing to eliminate algae growth in the tubes running from the sump to the unit and back. You will probably get the black algae, not the bright green algae that you see in and around the lighting canopy. Using the milky-white, semi-transparent hard, plastic tubing resulted in this build-up after six months or so.

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