Temperature is an important factor that must be controlled exactly and in the correct range for a reef to be successful. It is one of the first parameters that should be allowed for when considering the establishment of a reef tank.

Why is it that the temperature is such an important factor and has to be maintained in such a narrow range? There are several reasons:

The activity of enzymes.

Enzymes are used in various biological pathways within living organisms in order to catalyse or assist a reaction to take place. The shape of an enzyme is of vital importance to its ability to function correctly, with a slight temperature change having a huge impact on the shape of the enzyme molecule. This results from the fact that the shape of the enzyme is determined by hydrogen bonds (the sharing of a hydrogen atom between two parts of a molecule, usually two hydroxide groups, OH), and the tendency for hydrophobic (water hating) parts of the molecule to isolate itself from the surrounding water environment. These two forces that hold the enzyme in the correct shape are relatively weak and can be easily disrupted by a change in temperature. Once the shape of the enzyme is disrupted from that of its biologically active form, then it either performs its function at a reduced efficiency or no longer can perform it at all.

The demand and solubility of oxygen.

As the temperature increases, then the metabolic demand for oxygen also increases. But conversely the solubility of oxygen falls, with oxygen only being half as soluble at 30 ^O C as it is at 0 ^O C. Therefore an organism will have difficulty extracting enough oxygen from the water to keep its metabolic processes operating at elevated temperatures, above that which it is acclimatised to.

The temperature dependence of chemical reaction rates.

The biological chemical reactions that occur in a cell are highly complex, with many different ones in parallel and series occurring simultaneously. These reactions are all in balance, with the rate of each tuned such that there is no undue accumulation or depreciation of any one species within the reaction pathway. The reaction rate of each reaction is influenced by the temperature, with an increase in temperature typically increasing the rate at which the reaction proceeds. (It should be noted also that in the case of some reactions, a temperature increase may cause a decrease in the reaction rate.) And each reaction involved in a biological reaction pathway will have a slightly different rate change for a given temperature change. With a disturbance in the temperature, then these reaction pathways become unbalanced. As a result some products and reactants required become either depleted or in excess. This unbalancing can cause major problems with the health of the organism, possibly resulting in death when taken to the extreme.

The ideal temperature range for a tropical reef tank is from 21 to 27 ^O C. A swing of one or two degrees during the daily cycle with in a reef tank will not cause any undue stress to the tank inhabitants. But it is best to aim for a closer variation to that experienced in nature, which is typically measured in tenths of a degree in temperature change day to day. It should also be noted that a higher than normal temperature is more dangerous than one lower than normal.

What influences the temperature of a tank? Anything that has a different temperature to the tank, and comes into contact with it in some way, whether direct or indirect, will influence the water temperature. The following items will influence the temperature of a tank:

• Water heater
• Chiller
• Room temperature
• Heat generated by water pumps
• Heat input via the light globes
• Heat generated by the lighting ballasts
• Evaporation of tank water
• Convective cooling via the air blown over the water surface
• Convective cooling via the tank walls

In order to control the temperature of a reef tank, several methods can be utilised.

1. The one that first comes to mind are water heaters. When using a heater, make sure it is located in a high water flow area. Additionally, use more than one to achieve the required total wattage for the tank so that if one fails then the problem that it will cause will be minimised.
2. The simplest method, and most stable, of temperature control is having the tank stored in a temperature controlled room. This usually means the room is maintained at a constant temperature by air conditioning.
3. Evaporation of the system water can be used to lower the temperature. This is helped by using fans to move a high volume of air across the water surface, allowing more water to evaporate.
4. If evaporation is not enough to maintain a low enough temperature then a chiller can be used. A chiller is just a type of refrigerator that cools the system water. They are expensive, but if there is a large wattage of lighting over the tank then this will be the only way to keep the temperature down into a suitable range.

Q: Some people reccomend taking out or turning off of heater in summer, why, when it has a thermostat?

Well, I suspect the reasoning behind that is that the room temperature is always around that required to maintain the tanks temperature that you are aiming for. In that case then having a heater is not required. I have notice with my tank now that I am coming into summer is that it is only on during the night, and only for a short period of time too. DBW

Q: any suggestions on diy chillers and their effectiveness?

Good Q that one actually ;-) I am just in the middle of building a DIY chiller, and I have several different ways of doing it. The way I am making mine is a small fridge, turned onto its back and the compressor turned up the right way. I am going to fill the inside with salt water, this lowers the freezing point, and then use some polypropylene piping running through it which will carry the tank water through it. A powerhead will be connected to this to turn on via a DIY thermostat, another simple project. The plastic is not the most conductive material, but it is cheap. I have looked into glass, this is very expensive, AUD$15 per 30cm of tubing, and titanium cost an arm and a leg too. Another technique that you can do is to have the evaporator of the fridge, the bit that get cold, actually touching the side of the sump or tank, this works really well too. But this requires a bit more know how with fridges and refridgerants. DBW

Q: can you elaborate on the thermostat?

Well, I found a simple circuit online, I have it linked on my site, OZ REEF Marine Park, in the DIY Plans section. I am going to build it shortly, and when I have I will put full plans online, parts etc to make a full unit. I am going to use one of these as well for the fans over the top of my tank too. By the way, my URL is www.ecr.mu.oz.au/~dagley/ ........... DBW

Q: what about a sealed, plumbed glass tank fitting into the freezer section?

That may work, but you have a limited area for the heat transfer to occur over. I would have to do some calculations to see if it would be an improvement over the piping, but I suspect the piping would come out on top. DBW

Just a note on the way I am doing my chiller .... The entire compartment will be filled with water, that will mean there will be great heat transfer from the evaporator to the water, so this will be very efficient... Then this will be in contact with the tubing which will be throughout the entire compartment, with a couple of important heat exchange principles put in. Detail when I have it built. DBW

Q: do you know of any noticable effects on Calcium dissolution/precipitation related to temperature?

Well, have not had much of a think about that. But my thoughts on this currently would be ... At higher temperatures the solubility of calcium is higher, which is good for the hard corals. But also that means the the solubility of carbon dioxide is also lower, which is an important component of the carbonate buffering system. (refer to my earlier talk or article on my site about this) But over the temperature range that a reef operates I would suspect that it would not really have much effect that we should be worried about. DBW

Q: could you baffle the tank and have a slow return?

OK, I suspect this is still about the glass tank in the fridge for the chiller .... Baffling the tank would help, that would mean that the flow through the tnak would be more structured, making sure that some of the water does not short circuit it to the output on the tank before chiller enough. One thing with using a tank will mean that you will have to have two pumps, one in the main tank or sump, and one in the chiller to return the water. Other wise you will have to make the glass tank, inside the chiller, fully sealed. DBW

Q: how does temperature effect protein skimming?

Increasing T decreases the efficiency of skimming. There are several reasons for this: 1) Higher T means that the foam is less stable, because of the higher mobility of the surface active molecules and slightly high solubility in the salt water. Actually, that is two reasons inthe one, opps, should have separated it. Oh well. The two reason are then higher solubility of the surface active molecules, therefore the foam will be less stable. And also the higher mobility of the molecules. DBW

Thanks again for the great talk DBW. Visit DBW's OZ Reef site at www.ecr.mu.oz.au/~dagley