How would you design an in-wall reef aquarium so that a chiller would not be needed? It requires a bit of improvisation, but I accomplished this for a new client.

I received a phone call from a lady who needed me to move the contents of her 90-gallon, in-wall reef aquarium to a free-standing, 120-gallon aquarium in her new home. The gentleman who bought her old house requested an estimate for bringing the 90-gallon back into commission as a reef aquarium. The tank wasn't big, so I wanted to make sure that I made up for this by equipping it with great filtration and very bright lighting, all without causing too much heat to build up inside the cabinetry.

In Wall Reef Aquarium

In many cases, a chiller would be used to make certain the water temperature does not exceed 80° to 82°F, but not only was there zero space to add a chiller, it is also a huge mistake to put a chiller in a tight, enclosed, poorly ventilated space. A chiller dumps the heat that it removes to cool the water down, just like a window air conditioner, so it will seriously heat up the air in the cabinet. Also, the cooler the air it's allowed to draw in, the more efficiently it will cool the water.


Right away I knew I was going to use LED aquarium lights on this system. LED aquarium lights have come a long way since even a couple of years ago, and using T5 fluorescents or metal halides wouldn't have worked because too much heat would have been created inside the cabinetry. LEDs do produce some heat, but much less than either of the aforementioned light sources. When left on for an hour, a 150-watt metal halide bulb would burn your skin if touched, T5 fluorescents would be uncomfortably hot, and LED aquarium lighting would only be warm to the touch.


The former homeowner took all the filtration in the move, but that was fine because we had decided to upgrade anyway. For a year prior to setting up this reef system, I had been slowly adding solid carbon dosing to my clients' saltwater fish-only and reef systems to great effect. Solid carbon dosing is a method by which biodegradable plastic-like pellets are fluidized in a media reactor. The material the pellets are made from acts as both food source and colonizing surface for beneficial bacteria that consume nitrate and phosphate on a 1:1 basis.

It is important to place the effluent from the media reactor that you are using to fluidize the bio-pellets close to the intake of a protein skimmer. The bacteria are sloughed off of the surfaces of the pellets as they collide and are easily picked up by the skimmer, thus removing them, along with the nitrate and phosphate they utilized from the system.

People trying solid carbon dosing for the first time in an established saltwater aquarium quickly notice that their protein skimmer pulls out more and darker skimmate once the bacteria have established themselves. This may take around a month depending on whether you use a bacterial booster or not. To feed the bio-pellet reactor, I plumbed a fitting to branch off of the main pump and used a small ball valve to regulate the flow.

Choosing an external main pump in this situation was easy, since it is very well known that submersible pumps transfer much more heat to the aquarium water than do those that are mounted outside of the sump (a sump is a glass or acrylic tank that sits underneath the aquarium and houses all the filtration). I sized the main pump, choosing one that was pressure rated rather than volume rated.

Most external water pumps have two versions: volume-rated pumps and pressure-rated pumps. The pressure-rated pumps are designed to handle more back pressure without losing as much pumping volume as a volume-rated pump will. I always use pressure-rated pumps if I know that I am going to branch off of the main line to power a media reactor, push through a chiller, or run through an ultraviolet sterilizer. I also intentionally chose a pump that would move a couple hundred more gallons per hour (gph) than was required for the aquarium turnover rate, because I would be diverting that amount to power the media reactor.

Sump and Skimmer

The protein skimmer I used was a venturi-driven model with a needle wheel impeller. I used a space-saver model in which the water pump that powers the skimmer is located underneath it. This way, it takes up very little space in the small, acrylic sump.

The built-in, submersible pump that powers this skimmer uses very little electricity, especially when compared to older skimmer types that utilize a large, high-pressure pump that would only create more heat for the system to deal with. The acrylic sump was custom made to fit exactly the space I needed under the aquarium. I had it built to exact specs by a local fish store.

I employed a 100-micron filter bag where tile drain pipe coming from the aquarium brings water into the sump. This is a great way to polish the aquarium water and remove small particles floating around in the water column. Once a week or as needed, this bag is taken outside, hosed out with a pressure nozzle on a garden hose, wrung out to remove excess tap water, and put back into place.

Evaporative Loss Top-Off

I equipped the aquarium with an automatic evaporation top-off system in order to maintain a constant water level in the sump. As water evaporates from the system, an equal amount of fresh water is put back into the system. A sensor located in the sump tells a small, submersible pump located in the top-off reservoir when to turn on or shut off depending where the water level is in relation to this sensor.

Maintaining a constant water level in the sump is important both for the protein skimmer to work efficiently and to ensure that the main pump does not run dry. I keep the reservoir filled with purified water (RO/DI) because when water evaporates, it leaves behind nearly all of the substances dissolved in it. These substances are known as TDS (total dissolved solids) and include minerals such as calcium and magnesium carbonate and sodium chloride.

When a saltwater aquarium loses volume due to evaporation, it is fresh water that you must add back into the system, not salt water. This highly purified water has next to no mineral content or pH buffering ability, so l have the top-off go through a kalkwasser (calcium hydroxide) stirrer before entering the system.

If aquarium evaporation is too high, it can be dangerous to run kalkwasser in line with your top-off. You don't want to dose too much at one time, as it is a very caustic basic substance (pH of 12 after initial mixing with water). To prevent overdosing, I only keep about a tablespoon of calcium hydroxide in the stirrer at any given time. Between this and bi-weekly water changes (10 gallons at a time), all the necessary elements required by soft corals and large-polyped stony (LPS) corals are taken care of.

This system was designed to evaporate at a great rate because one of the best ways to cool water temperature down is through the use of fans blowing across the water surface, which causes massive evaporation. Besides the previously mentioned exhaust fan in the ceiling above the lights, I also ventilated the bottom cabinetry to help remove hot, humid air. I cut out a square in the drywall, installed a ventilation grate, and mounted a quiet, 4-inch fan that blows out of this grate.


Though no chiller was used to cool the water, a heater was necessary to keep the water temperature from dropping too low at night in the cooler months. Here in southeast Texas winters are not usually very cold, but we do experience temperature swings during the fall and winter that can catch an aquarium off guard and cause its inhabitants' lower, making immune systems to lower, making them more susceptible to parasites and diseases.

Therefore, I use a heater as at safety net to ensure that the temperature does not get too low. I use an external heater controller instead of relying on the controls inside the heater. A heater is no place to skimp. When your aquarium contains several thousand dollars of sensitive corals and fish, you don't want to leave things to chance.

Overview of Installation

By using energy-efficient LED aquarium lighting with a strong-yet-quiet bathroom exhaust fan mounted in the ceiling, external water pumps instead of submersible, and ventilating the cabinet below where the filtration is located, I was able to avoid installing a chiller or this system. The ambient temperature in the house stays around 76°, and the water temperature of the 90-gallon, in-wall reef averages 80° to 82°. To find out more, you can check out In Wall Reef Aquarium.