Marine Tank Ecology Name:_________________________

An ecoystem is a system in which biotic and abiotic factors cycle, creating a sustaining cycle. In nature, no true ecosystem exists as there is always some flow of nutrients, food and energy into or out of the system. Likewise, most tanks are not true ecosystems as humans must provide food and nutrients and sometimes remove wastes. While they don’t qualify as true ecosystems, they do involve a great deal of cycling and a well-designed tank has a complete nitrogen and phosphorus cycle.

Nitrogen Cycle: In many systems, nitrogen is a limiting factor. For example, the corn fields and green lawns around Brandon are usually starving for nitrogen. If we want them to grow, we must apply a fertilizer that supplies nitrogen. It is rather ironic that nitrogen can be a limiting factor as the air around us is composed of nearly 78% nitrogen. Atmospheric nitrogen is diatomic, with the two atoms covalently bound with a triple bond (very tightly bound together). Most plants and animals cannot break the triple bonds, leaving atmospheric nitrogen unavailable to living things. Some bacteria can use this nitrogen, known as nitrogen-fixing bacteria. Where do they live? In the roots of plants called legumes, such as beans, clovers and peanuts. Farmers often rotate crops, putting soybeans or clover in a field ever two or three years to better supply the soil with nitrogen.

To properly manage a tank, the nitrogen cycle must be understood. We introduce nitrogen in the form of the food we add (frozen brine shrimp, squid, seaweed, etc). Fish eat the food and excrete the waste as ammonia (NH3 or NH4). Ammonia can be used by plants and algae as a fertilizer after a different group of bacteria break it down into nitrite (NO3) and, finally, into nitrate (NO2). You may have heard of anhydrous ammonia being used by local farmers will add nitrogen to their soil (also used by young high school punks to make meth). In a tank, ammonia is toxic in high concentrations. If you start a tank and add a large number of fish, ammonia levels will spike due to the waste products of the fish. Why doesn’t this happen in an established tank? Bacteria (living in the sand, live rock and filter) break ammonia down to nitrite (harmful) and nitrate (which is harmless to fish).

So the cycle is as follows: Food (containing nitrogen is added) – fish digest it into ammonia (a toxic compound in a tank – ammonia levels should be near zero) – bacteria break ammonia into nitrite (another toxic chemical that should be kept nonexistent in a tank) – another group of bacteria break nitrite into nitrate (which can be used as a fertilizer by algae and plants, so moderate levels are fine in tank. See the diagram on pages 2 & 3 to get an overview of the nitrogen cycle in a tank.

What can one do to keep nitrogen levels low?

1) Don’t overfeed. The number one cause of tank deaths is due to overfeeding. The food that isn’t eaten is broken down into ammonia and then nitrite by bacteria, and these byproducts will kill the members of the tank.

2) Limit the number of living organisms in a tank. If too many living things are in a tank, there will be no way to keep up with the nitrogen load.

3) Add plenty of sand and live rock. These materials have plenty of surface area and provide a surface on which bacteria can live. Also don’t let the sand get too deep or there will be inadequate oxygen to keep the bacteria alive.

4) Keep the filter clean so debris doesn’t clog the material, keeping bacteria from getting adequate oxygen and water.

5) Allow a tank to age, allowing bacteria populations to grow adequately before adding too many living organisms.

Phosphorus Cycle: The food added to a tank also contain phosphorus. Like nitrogen, phosphorus is needed by plants and algae for fertilizer, but too much will result in excess algae growth or even poisoning of the tank.

Calcium Cycle: We need to monitor calcium levels as the algae and corals in marine tanks need the calcium to make a solid shell (the purple coating on the rocks is a marine algae that incorporates calcium into its body, thus called calcareous algae). We add calcium in liquid form, and need to replenish it after its levels fall due to being incorporated by algae and corals.