In the Beginning - June 18, 2005
The defining feature of Tidal Gardens is its greenhouse aquaculture facility. It houses three 1,000-gallon reef systems. There are several benefits to using a greenhouse for growing large volumes of coral.
First, it provides arguably the best light available. Some aquarists spend a great deal of time and money assembling complex lighting systems complete with timers and moonlight effects. One can argue that a greenhouse is essentially the perfect light on the perfect timer with practically no maintenance.
The second benefit is the greenhouse's resistance to water damage. Large volumes of salt water can really damage the immediate surroundings of standard construction. Salt spray and humidity (especially considering the volume of water involved) would make quick work of most residential style buildings.
Lastly, the greenhouse provides a very temperature stable environment for the corals. Even on cold winter days, the greenhouse is a warm 80 degrees when the sun comes out. It is only during the cold winter nights that the gas furnace activates.
The greenhouse setup drew a great deal of interest, so we decided to give our readers an inside look at the process of building a greenhouse for coral reef aquaculture. It came with its own set of unique challenges, but the finished product was very rewarding.
The Greenhouse Construction
Construction of the greenhouse began in the middle of 2003.
The greenhouse is made from polycarbonate structural sheet and an aluminum frame. The company that supplied the greenhouse kit likened the construction to building a fence. In theory, if you can build a fence, you should be able to make a greenhouse. Unfortunately, we do not have the luxury of living in a theoretical world. After having built a fence, I can safely say that a greenhouse is a LOT more difficult, and we were quick to call in the contractors to assemble the kit.
The structural sheet is made up of two thin layers of rigid polycarbonate with an air gap in the middle. The air gap provides insulation.
Several options for greenhouse materials were available, and it was decided the most robust materials would be the best choice long term. The winters in Ohio can be harsh, and it was important that the greenhouse be structurally stable as well as thermally stable over the cold months.
A single gas-powered furnace provides the heating. It heats both the air and the water in the tanks through a collection of heat coils. Tank water is pumped from the aquaculture systems to the output of the furnace and sent back to the tank. On the coldest winter days, the reef systems comfortably maintain a temperature of 78 degrees F. The warmth of the water in turn provides passive heat to the rest of the greenhouse. 3,000 gallons of near 80-degree water is a very effective heat sink.
In the summer months, the temperature can reach into the 90s. The greenhouse is ventilated by a 48" exhaust fan.
When it blows, the entire greenhouse becomes a wind tunnel and the heat and humidity that built up quickly dissipates.
When considering the construction of a greenhouse it is important to factor in the height of the greenhouse and the weather in the area. The Tidal Gardens greenhouse measures 56' x 24' and is 12' tall at its highest point. The taller the greenhouse, the better it can handle hot weather as heat rises and the temperature around the tanks is lower as a result. A taller greenhouse however will cost significantly more to heat in the winter.
The greenhouse is fed water from a well. In a perfect world, the water would be very low in contaminates right out of the faucet, but we were not so fortunate. Reef systems require clean water before mixing into salt water, and the water from the well was anything but clean. A total dissolved solids test (TDS) showed a reading of over 900ppm. This was an astronomically high reading considering there is a general rule in the hobby that any reading over 100ppm is highly suspect.
To reduce the well water's high TDS, the Tidal Gardens required a commercial scale water purification system. We decided on a 1,000 gallon per day Spectrapure Reverse Osmosis (RO) system.
The large cylinders to the left of the RO unit are the prefilters. There is a dedicated carbon prefilter, and two stages of water softening. Soft water is much easier on RO membranes and a softener greatly extends the life of the membrane. For small scale hobby purposes, this is not a major benefit, but on a commercial scale, a water softener becomes a cost effective solution to frequently replacing a 1,000 gallon per day RO membrane.
After the purification system was installed, the TDS of the output water was reduced to 2.3ppm. It would be possible to reduce that TDS down to zero with the addition of a deionization (DI) filter, but it was decided that 2.3 was adequate without the additional expense of a large DI filter.
All sorts of tanks are available. We considered glass, acrylic, fiberglass, plastic, and rubber pond liners. There were two main criteria for the tanks. They had to be cheap, and they had to be robust.
Right away, pond liner was out of the question. It is inexpensive, but it was the least likely to hold up well over time. The chief concerns were burrowing organisms and UV degradation. On the other end of the spectrum, glass and acrylic tanks were eliminated due to their cost.
The decision came down to fiberglass and plastic. Aquatic Ecosystems sells 1000-gallon fiberglass raceways. While beautiful, they were too expensive to justify.
The closest substitute was the 300-gallon Rubbermaid stock tank. They have a nice sturdy body, and could be purchased for less than $1 per gallon.
Though we decided glass tanks were not practical to use as aquaculture tanks, we decided to use two glass aquariums on each system so we would be able to photograph corals more easily.
In the end, each aquaculture system consisted of:
- Two 300-gallon Stock Tanks
- One 150-gallon Stack Tank
- Two 125-gallon Glass Aquariums
Each system is equipped with a large skimmer. Two of the systems use a 12" diameter needle wheel skimmer. They stand roughly 48" tall and do an excellent job skimming. The nice thing about the needle wheel skimmers is the simplicity of the design. It is easy to quickly take them apart for maintenance.
The last system uses a very large self-cleaning skimmer made by RK2. It stands a good 7 feet tall and has a set of spray injectors to periodically clean the inside and outside of the skimmer collection cup. While not as simple as the needle wheel skimmers on the other systems, the RK2 is actually less maintenance because so much of it is automated.