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.
Water Quality
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.
Aquaculture Tanks
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
Filtration
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.
Greenhouse Update - June 28, 2007
If there is ever a bright side to losing countless corals in a blizzard, it is the opportunity to fix all the little mistakes
that only become apparent after years of operation. Before, when the systems were thriving and full of coral, things were pretty much set in stone, and no large-scale changes were possible. As unfortunate as the blizzard was, it did act as a reset switch that allowed us to go back and actually implement some changes to improve things going forward that would otherwise be next to impossible.
The major problem we've had the past three years has been heating the greenhouse in the winter. Up to this point, a central gas
furnace heated both the air and tank water. Water pumps would send tank water to the heater to get warmed and then return to the systems. On the coldest sub-zero
days, the water temperature would not dip below 70-degrees Fahrenheit.
There were two problems with this setup however. First, the cost of running the heater was excessive. It was not uncommon to have a monthly bill of over $1000 during the winter months. Second, this was the only source of heat, so if something were to happen to the furnace, the systems
were in serious danger. The greenhouse
has electrical backup however there was nothing to restart the gas furnace once its pilot light blew out. The next greenhouse
setup had to remedy both of these problems.
 |
| 4" thick foam insulation and wire mesh |
A heated concrete floor was the most elegant solution to our heating issues. It would operate in conjunction with the main gas
furnace to provide heat to the green
house for redundancy. Also, the method of heating is supposedly far more energy efficient, so hopefully it will reduce the gas
bills to triple digits.
The construction began first with emptying the greenhouse of the tanks sitting on the ground as well as all the plants.
In the picture, a 4" foam pad was installed into the floor to provide insulation and the metal mesh laid on top.
The glass tanks are resting on concrete block pillars. They are going to remain in operation during the construction because all
the live rock and remaining coral still need a place to live. While most of the coral died, a surprising number of invertebrates in the rocks survived as well as
some peppermint shrimp.
 |
| Red polyethylene tubing will carry water that will heat and cool the greenhouse depending on the season. |
Once the insulation and wire mesh was laid down, the red heating coils were installed. The tubing was made from polyethylene,
and all these tubes converge on a central manifold.
In the winter months, heated water will flow through the tubing, which in turn will heat the concrete providing radiant heat
evenly throughout the greenhouse. In the summer months, the opposite is true. Cold water from the well will flow through the tubing creating a cooling effect. The
water coming out of the well is roughly 50 degrees Fahrenheit, and so far, the difference is noticeable. Before, we would experience 85 degree water on the hottest
days however after the flooring was installed, the temperate in the water does not exceed 81 degrees.
 |
| Pouring cement while the reef tanks were still in operation. |
As one can imagine, the tanks underwent some stress during the construction. First off, the only form of circulation was a
single pump sending water to a spray bar. The skimmers were taken offline as well because they are usually installed in a maintenance tank that sits on the ground.
To further complicate things, it was blazing hot for the week or so that the floor was being installed, and it was not uncommon
for the water temperature to reach almost 90 degrees Fahrenheit. Normally when the system is attached to the tanks sitting on the ground, the temperature does not
rise about 85 degrees Fahrenheit.
 |
| Yes, the heating system really is that complicated. |
The manifold on pictured on the left is still a bit of a mystery to me. The contractor that installed it for us admitted that
it was by far the most complex installation he had ever done. I would try and explain it all, but in the end it would probably be wrong and I would just be
confused. The end product is a cold floor i
n the summer and a warm floor in the winter. I'm happy with that, and hopefully the corals will be as well.
 |
| Lifting semi-full 125-gallon aquariums is easily the most frightening thing I've ever done in this hobby. |
Once the concrete was poured and hardened, the really scary task awaited. The new floor was roughly 4" higher than the original
floor. The tanks that sit on the ground are arranged in such a way that a portion of them fits under the glass aquariums. The raised floor however no longer
allows the tanks to fit under the aquariums, so they must be lifted several inches. We used a very old hydraulic lift and some muscle to fit in an additional concrete
block into each of the pillars. I was terrified that the glass would shatter on a number of occasions or the lift would simply fail, however neither happened
thankfully.
 |
| Finally, the concrete is set and the tanks are put back in place. |
At last the tanks are back in place and the systems restarted with a fresh batch of salt water. For each of the three systems,
750 gallons of new water was made.
It has been about 3 weeks since construction wrapped up and everything passed code. The tanks are stable once again with a
minimal amount of nuisance algae. In the next few weeks we will be adding new stock from as many propagated sources as possible.
Although the blizzard was a major disappointment, it gave us an opportunity to improve on the greenhouse. We've often started
sentences, "if we could have done this differently from the beginning we would have..." Through some unfortunate circumstances, we've actually had that chance to
restart and it has turned out well.
Greenhouse Update - August 15, 2009
Each year in an effort to improve the greenhouse we plan some modest projects. Some years we do something more elaborate for example in 2007 we installed the new heated floor. 2009 is another year in which we implemented some major changes to the greenhouse to make it
better. Our focus this time around was directed toward heating and cooling efficiency.
The first major change we made was the walls and ceilings of the greenhouse. For 5 years now, a single pane of double-walled polycarbonate has made up the greenhouse walls. Initially heating the greenhouse was a bit of a challenge as a result of heat loss through the
walls and ceiling. This year we finally committed to installing a second layer of double-walled glazing to the entire greenhouse.
 |
| The walls are now much more thermally stable in preparation for the cold winters ahead |
Adding a second layer of glazing would in essence create three air gaps for insulation, one in the outer pane, one in the inner pane, and a large gap in between the two sheets of glazing. The hope is, once the second layer of glazing goes up, the heating bill in the
winter would drop significantly. A single panel of 8mm double-wall polycarbonate has an R-Value of 1.6. By adding the second panel, I suspect we would more than triple the R-Value of the wall to something in the neighborhood of 5.0. An R-Value of 5.0 is roughly
equivalent to 1.5" of polystyrene foam.
Installing the second layer of glazing was a lot of work but luckily we got a lot of help from friends and family. The ceiling installation was professionally done and the final product was very nice.
 |
| A view of the new vent from outside the greenhouse |
While the first change was made to better address heating bills in the winter, the second change was done to lower the cooling bill in the summer. Frankly, the cooling bills in the summer were never that high to begin with, but the greenhouse itself on certain summer days
was unbearable to work in and the temperature in the tanks approached 90 degrees. The large 48” exhaust fan did a great job of moving air at the level of the fan however heat would quickly build in the upper regions of the greenhouse and cause the building as a
whole to be uncomfortably warm whenever there was direct sunlight. While we were working on installing the second layer of glazing on the ceiling of the greenhouse, we could feel the temperature increase 10 degrees every few feet. It was probably close to 150 degrees F
at the top of the greenhouse.
 |
| A view from inside. The black piston shown controls the opening and closing of the vent |
To combat this heat issue, we decided to look into automatic vents at the top of the greenhouse. Farmtek sells a very elegant automatic vent system. When I first saw the item in the catalog, I was thinking it was an electrical device on a thermostat but in reality these
units are not hooked up in any way to an electrical source. The vents are opened and closed by a black piston filled with a special fluid. When the temperature rises, the fluid in the piston expands causing the vent to open. Once the heat in the building escapes the
fluid in the piston cools and the vent closes. We installed three of these vents and the impact was immediately noticeable. What was once an uncomfortably hot greenhouse in the summer became a very pleasant one.
The exhaust fans now come on half as often and almost never run full blast. In past summers, the main exhaust fan typically ran at 100% for at least five hours a day. The fan is a 10-amp unit so one can imagine the electrical draw. Now that the vents in the roof are in
place, the main exhaust fan stays inactive for much of the day and practically never has to run at 100%.
