Letter 031115 - The beauty of a reef tank
First I should mention that I wrote this as you can see 2003-03-15 and I did not finish it. But as I think it can be valuable to someone I publish it here now (2004-09-18) in it's unfinished state anyway. I plan to finish it someday though :) .
I have a hobby that I am definetely going to pick up one day again when I have the space. That is aquariums or more specifically the marine aquarium (salt water aquarium). The often used term reef aquarium or reef tank means an aquarium that is set in an Coral Reef environment.
I decided to write a small letter describing my interest, but as I started it was so fun that I just had to make this a larger piece of work than was first intended. Hope someone can enyoy it as much as I enjoyed writing it :) Anyway here is a small index of the different sections...
Why am I so interested in this hobby ?
Introduction to the Reef Systems
Where are the reefs ?
The light
The temperature
The motion
The chemistry
Phosphorus
Nitrogen
Carbon
Why am I so interested in this hobby ?
The first thing that strucks you when seeing a good maintained reef tank is it's beuty, which makes me think of a text I read on the web by Homer Wilson Smith and Jane Elizabeth Staller in 1997 about the then very hype subject of mathematical fractals.
"The Beauty Pinciple says that if a theory or principle is
beautiful or elegant then it has a high probability of being true and
useful."
So this image I first have of a beuatiful reef tank does not only represent the beuty in itself but the beuty of a living system of science. There are also more connections to be made between fractals and a reef tank, but I will come back to that later.
So not very far-fetched the second thing that makes it so interesting is the biology and chemistry that lies behind what you see. Reading about the reef ecosystem and the biology of soft and hard corals is very interesting in itself. The book...
"The Reef Aquarium: A Comprehensive Guide to the Identification and Care of Tropical Marine Invertebrates, Volume 1" by J. Charles Delbeek and Julian Sprung has a very thorough introduction in the area. I will also write some more about the biology, chemistry and ecology of a reef system later.
And thirdly the set up of a marine tank requires technology and physics. You certainly want a tank that is easy to maintain and that prevents disasters if anything should go wrong.
So you see that it's many fields that you touch in this hobby, and that is what makes it so fun.
Introduction to the Reef Systems
- Where are the reefs ?
Where are the reefs located that we are trying to replicate at home ? There are two main prerequisitives that makes a location possible for a coral reef; which is high water temperatures and bright light. These conditions are mainly fulfilled in the 60 degree area between 30°S and 30°N with a few exceptions. In general the areas with greatest growth of corals are in waters with surface temperatures between 25 °C and 30 °C.
- The light
The brightness of the sun at the equator is very very high. About 130 000 Lux at peak values of the day. Should we generate 130 000 Lux in the aquarium? It could be interesting to figure out how many watts that is. But there are no definite conversion scale between lux and watts because how many watts a lux are depends on the wavelength of the light. But to take one simple example, one ordinary light bulb generates about 0.5 Lux per watt. So that would mean that we needed 260 000 Watts of light bulbs to get the intensity of the sun at the equator. This would indeed be an expensive aquarium to run. (It should be mentioned that 1 Lux is the intensity over 1 square meter. ) But there are losses in the intensity of the light, firstly much of the light are reflected away by the water surface such that right below the surface only about 70 000 Lux remains. Then the intensity drops rapidly as we go deeper in the water. At 5 meters depth the intesity of the light is about 26 000 Lux and at 10 meters about 17 000 Lux. At 100 meters there are only about 50 Lux remaining. Modern Metal Halide lighting produces about 80 Lux per Watt, thus to simulate the peak brightness at 5 meters depth we need 26000/80=325 Watts of MH lighting.
*Temperatures*
- The temperature
Of course the marine fauna exists at highly variated temperatures, but as I am going to focus on the coral reefs in the range described earlier the temperatures fall in the range (25°C to 30°C) throughout the year. A too high temperature is worse than a low so in the aquariums you should adjust to somewhere in the range of (21°C to 27°C) and ideally a temperature can be (23°C to 24°). But it should be mentioned that there are coral reefs in colder waters and that it's possible to start a cold water marine aquarium. (See for example -
Skjærgårds akvariet
) There are many more chemical values to look after in a marine tank which is described further down but the temperature is in fact the most important one. A tip is that a larger uncovered surface area cools the aquarium due to evaporative cooling. (A nice applet describing evaporative cooling can be seen here:
evaporative_cooling, and there is a nice little discussion about Bohr-Einstein-Condensate there also... ehm this letter is going to take time to write, I constantly jump away in small threads like this one ;) )
As I have not mentioned (but should do) it's often easier with a larger aquarium than a small one, even when conserning the temperature. Imagine the temperature in the oceans, does it fluctuate several degrees between night and day ? No water is unique in that it absorbs large amounts of heat without much alteration in its temperature. But this do not hold as well for a minimal aquarium, the smaller aquarium you have the larger will the fluctuations in temperature become and a heater or chiller with capacity to maintain the temperature may be needed. In a larger aquarium the temperature changes much more slowly which more naturally imitates the situation in the sea.
I did mention a chiller. May that really be necessary ? Well that depends, if you are running your aquarium at 26°C you may seem that that is a quite high temperature, but if you hold light demanding corals and look back at the light section of this letter you may figure out that all those Watts generate heat, and in addition the circulation pumps and skimmer (which will be desribed later) together adds quite alot of energy. But this is something you just have to check when you set up the aquarium if you need heaters or chillers or maybe you can do without both these. Chillers are very expensive so to stay out of those would be nice for your wallet. And a small tip regarding heaters, escpecially if you have a small aquarium; imagine you are recommended 200W of heating to keep the temperature up to the desired level don't buy a 200W heater, but instead get 2x100W. The reason is that there is always the possibility that the thermostat malfunctions and the heter get stuck in on-position. If this is the case and you use a single 200W there is a possibility that it heats up your aquarium to dangerous temperatures for the life you maintain in it. Using 2x100W and one gets stuck the other one shuts off, and you have only a constant heating of 100W which at leasts make the danger come not so fast if it come at all.
- Water motion
If you sometime have kept a tropic freshwater aquarium (which so many of us have) you may remember the single pump that you probably used as a filter which stirred the water gently.
The environment where we find the fish in the tropical freshwater tanks are mosly inland lakes where the water motion is not large. The situation on the coral reef is another, the water motion is much higher. If you refer to the litterature there are different numbers figurating of the need for water motion in the aquarium, but generally a turn over of 6-10 times the aquarium volume is recommended. That means that you should use pumps with a total capacity that pumps the volume of the aquarium 6 to 10 times in an hour. For example a 300 liters aquarium with a turnover of 8 would use pumps with a total capacity of 2400 liters an hour. It's also a good idea to variate the motion in the aquarium such for various reasons, for example the same motion all the time would probably collect all waste at the same areas. One simple solution to this is just to set the differnet pumps on timers. (There are of course more expenive and clever solutions to this for those who want.)But even as most marine aquaria requires much motion in the water it can't be taken as a 100 % rule, for example seahorses does not like much motion.
- The Chemistry
The goal with maintaining a marine aquarium is of course to get a system that is as natural as possible. But to understand it all I thought I should go through some of the chemsitry in the aquarium first.
Firstly the water around the coral reefs is quite nutrient poor which explains the beautiful clarity of the water. What nutrients are there that the aquatic organisms live of ?
- Nitrogen (N)
- Ammonium - (NH4+)
- Nitrite - (NO2-)
- Nitrate - (NO3-)
- Phosphorus - (PO4-3)
- Carbon - (C)
For example the values in the summer for the Great Barrier Reef are...
 |
| Ammonium | Nitrite | Nitrate | Phosphate |
| 0.004 | 0.0009 | 0.03 | 0.03 |
Amounts in mg/liter |
Some new nutrients are though replenished by the seawater in areas of upwelling (where nutrient rich deep water flows up), this upwelling can occur near islands as the water in the deep currents are forced to bend uppwards. Some upwelling also occurs when the wind blows away the surface water and thus makes the deeper water rise.
Nutritients can also come via fresh water rivers for reefs that are located nearby. Other sources are fishs and birds that transport nutritients from other areas.
Lets first look at Phosphorus
In every living creature there are phosphorus (from now on called P). P is one of the basic building blocks of living matter. It's one of the six elements that make up 98% of living organisms (H,O,N,C,P and S), and plays a role in the essential deoxyribonucleic acid (DNA), ribonucleic acid (RNA), adenosine diphosphate (ADP), and adenosine triphosphate (ATP). Phosphorus is the eleventh-most abundant mineral in the earth's crust and does not exist in a gaseous state.
But excess values of P can result in two undecirable results for the reef keeper (you), the first is that P is algae's best friend, and secondly is that it can inhibit calcification by corals and coralline algae. Due to this two things it's essential to keep the P levels in control.
Though it can sometimes be hard to prrof that P is the reason behind excessive algae growth as sometimes the algae grows so fast that it converts the p in the water as fast as it enters. But if you have unnormal high algae growth you can at least suspect mr P.
So when we talk about a nutrient in the tank we have to look at some aspects. How does it increase and decrease in concentration, or how does it enter and leave the tank ?
As organic material contains P one source for P to enter the tank is through the feeding. And even if the fishies eat all the food you provide them there are P in the excretion from them. Another source of P may be your tap water if you do not treat it before adding it to the aquaria.
The P in the tank is either taken up in living organisms such as fish, corals and bacteria, or deposited in the sediment, such as onto live rock(will be covered later) and sand.
So how do you lower high levels of P ? Here are 5 methods...
- Macroalgae - You can either grow this type of algae in a separate refugium tank (connected to the main tank) or have them in the main tank. As these algae groe fast they take up P fast from the water.
- Skimming - This also reduces the P levels as it reduces organic forms of P. The skimmer will be covered later in more detail.
- Limewater - Addition of limewater (high pH makes P bind to rock and sand)
- There are also special P reducing additions to buy from your dealer
- Keeping the pH high (8.4), but beware when the pH lowers!
Ok that was phosphorus, lets now examine the role of Nitrogen (or N).
Nitrogen makes up 78% of the atmosphere as gaseous molecular nitrogen and is also a constituent of all living tissues. Nitrogen is an essential part of amino and nucleic acids which makes nitrogen vital to all life. Nitrate and nitrite are inorganic ions occurring naturally as part of the nitrogen cycle.
Nitrogen takes many forms in the oceans, and we need to know about the following: Gas (N
2), Ammonia (NH
3/NH
4+), Nitrite (NO
2-) and Nitrate (NO
3-).
Earlier in the history of aquarium keeping frequent water changes was made with one of it's primary goals to reduce the level of nitrate in the aquaria. Modern aquaria suffers less from this. Nitrate in it self are not very toxic, but it increases the algae growth and also spur the growth of zooxhanthellae (which is an important part for so called hermatypic corals, excessive zooxhanthellae growth can decrease the growth rate of the host coral). So to keep nitrate levels low is of importance. You should keep levels below 20ppm, but preferably even lower (below 1ppm)
Ammonia is very toxic to the life in the aquarium, and levels of ammonia should always measure zero in a flully cycled tank.
Nitrite is only slightly less toxic than ammonia ans should always measure zero.
The process of nitrification is an important aspect and I am briefly going through it. In this process bacteria called
Nitrosomonas spp. oxidizes ammonia into nitrite. The nitrite in turn is oxidized by
Nitrobacter spp. into nitrate.
The process of denitrification goes the other way and here bacteria reduces nitrate to nitrite and eventually to ammonium producing nitrogen and nitrous oxide gases as waste.
I tried to illustrate the Nitrogen Cycle in the image below. I wanted to make it easy but at the same time not loose anything important. Well it resulted in what you see below :) The nitrification follows the blue arrows while the denitrification follows the red arrows.
One important thing to be very aware of when starting up a reef aquarium is to not haste. The aquarium must stabilize and we call this to cycle the tank. Never introduce many or any sensitive fish or coral before the tank is fully cycled. But if you want you can speed the process up by introducing one or two hardy fishes that produces ammonia. By understanding the nitrogen cycle you can understand the levels in the graph below.
At first you will have very few bacteria in your tank so the levels of toxic ammonia will ride steady. All around us both in water and air are the small nitrosomonas bacteria. As the levels of ammonia increases there are more food for the nitrosomonas and they will become more and more numerous. This will slowly begin to rise the levels of nitrite as the nitrosomonas converts the ammonia to nitrite. This in turn will gain the nitrobacter colonies which converts nitrite to nitrate. After a certain amount of time the nitrite and ammonia levels should be nearly zero and you have a fully cycled tank. But beware of the nitrate levels. There are some different methods to lower the amount of nitrate in your tank...
- Reduce import ! - Stop overfeeding !
- Increase export I ! - This can be done by proper skimmin techniques (as will be described later)
- Increase export II ! - Grow macroalgae and harvest
- Deep sand beds can be used. As a deep layer of sand creates anaerob conditions where nitrate can be converted to N2
There are more ways to reduce the levels of nitrate in the aquaria but these are the simplest in my opinion.
So that was N. So on to the next element which also is one of the very important building block of life. All organic compounds contains carbon. C is very important for reefs as it's built by carbon in combination with calcium, strontium and magnesium.
***MORE HERE***
Other variables to look after in a marine aquarium is...
pH
This measures the concentration of hydogen (H
+) and hydroxide (OH
-) ions. The logarithmic scale goes from 0 to 14 where a pH of 7 is called neutral and below 7 acid (higher conc. of H
+), and values above 7 are basic. Pure water has a pH of 7. Different fish lives in different pH values and can survive in a pH range 5.0 - 9.5. In a freshwater tank the pH is often slightly acidic for egg laying fish (6.5-7.0) or slightly alkaline for live-bearing fish. Seawater has a pH of 8.0-8.25, but in a reef aquarium optimal pH is on the range 8.2 to 8.5. Survival range is a bit wider (7.6 - 9.0). Onto the next...
Alkalinity
Alkalinity is the ability to neutralize acids. Total alkalinity is the total concentration of bases in water. Alkalinity is provided by various negatively charged ionic compounds (anions). Carbonate hardness is a term related to the alkalinity but only measures the carbonate portions. The alkalinity is of importance as it can be thought of as a sort of defense system for the pH value. A high alkalinity value makes drops in the pH value slower and thus prevents rapid swings. This is called a buffering effect. But the alkalinity is being used up and when it's exhausted you can excperience a rapid change. There are unfortunately several scales in use to measure the alkalinity, mg/l, ppm, dKH or meq/l. Values should be in the range 2.5 to 3.5 meq/l or 7 to 10 dKH. Commercial buffers or additions of kalkwasser can maintain the alkalinity level in your tank.
Salinity
As we are discussing marine aquariums, one important fact id of course the salt in the saltwater. The amount of salt in water can be measured by two techniques, Specific Gravity (SG) with a hydrometer or Conductivity (C) with an electronic probe. Specifig gravity measures the density of the water, distilled water has a SG of 1.000 while seawater is in the range 1.022 to 1.030.
Dissolved Oxygen
Carbonate Hardness
Trace Elements
Sources
http://www.advancedaquarist.com
http://h2osparc.wq.ncsu.edu
http://en.wikipedia.org
http://www.blc.arizona.edu
http://www.fishprofiles.net/
http://www.versaquatics.com/
http://www.reefcorner.com/
http://www.animalnetwork.com/
http://www.aaawatertesting.com/
