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Ultra-Violet Sterilizers

The Nitrogen Cycle - Aquarium Cycle

Reverse Osmosis - Water Purification

De-Ionization - Water Purification

 
UV Sterilizers
Ultra-violet sterilizers are used for multiple applications. They are used in water sterilization for drinking, hospitals and disinfecting. UV Radiation will kill almost anything. Do not look directly at a UV light because it can cause you to go blind. The sun emits UV light in small quantities. UV light can be good for our skin in small amounts, but prolonged exposure will lead to burning. That's what all the hype about the ozone (O3) layer is about. The Ozone layer blocks the majority of UV light entering our atmosphere. UV light is good for corals too. It's what gives them their color (more on this in the lighting section) but too much UV can burn them too! A UV light is a light that emits only UV and very little visible light. A UV sterilizer is a sealed unit that houses a UV light. It is normally in a tube shape made of UV-resistant material that allows water to pass through it. The bulb is sometimes sealed inside the unit so water can pass directly over it. In some cases, a quartz sleeve surrounds the bulb. This allows for easier replacement. The quartz unit is much more expensive but well worth the price for ease of maintenance. Quartz is used instead of glass or plastic because they block UV light. As the water passes through the UV sterilizer, all bacteria algae and viruses are destroyed. This keeps the water clear and reduces the risk of the animals contracting disease. In reef aquariums, some people don't like to use UV sterilizers because they can kill plankton. Plankton like minerals and vitamins can now be supplemented, so this is not a worry. Back to top
 
 
The Nitrogen Cycle

When food or any organic material for that matter is introduced to the tank it becomes waste through one way or another, waste in the form of NH4+ (ammonium) and NH3 (ammonia). Ammonium is a non-toxic nitrogenous compound. In marine aquariums were the pH is high (more than 7.0), ammonium releases a hydrogen ion (H+) to create NH3 (ammonia). NH3 + H+ ? NH4+ (low pH, <7.0) NH4+ + OH- ? NH3 + H2O (high pH, >7.0) As we all know ammonia is very toxic, and it will actually burn the delicate slime layers and gills of the animals in our aquarium. Even the slightest trace of ammonia could be deadly to any marine life. After a tank has been running for a few days with some sort of bio load, be it fishes, mollusks, econoderms or the like, ammonia begins to build up. This is why we use hearty animals when starting a new aquarium they can more safely tolerate these conditions. We can test for ammonia with a simple inexpensive kit. Unfortunately they only test total ammonia. Total ammonia is sum concentration of ammonia and ammonium. As we all know now ammonium is non toxic so unless there are major pH changes we are not too worried about our ammonium concentration. How do we get rid of ammonia? As the concentrations of ammonia become higher bacteria that oxidize ammonia for energy begin to multiply. Now I know what you're thinking. No, you don't have to introduce bacteria into your aquarium. Yes, it does speed up the process somewhat, but it is not essential. Bacteria are all over the place; on your hands, in the air, and it will quickly adapt to live in your new aquarium. These bacteria (Nitrosomonas) will "consume" the NH3 and expel NO2 (Nitrite), thru a process we call oxidation. Nitrosomonas are very similar to the bacteria that oxidized your 1972 beetle. Don't get scared by the formulas, they are very extraneous.

NH4+ + 2O2 = NO2 + 2H2O + energy

4NH3 + 7O2 = 4NO2 + 6H2O + energy

Nitrite is also very toxic, causing a condition in fishes known as, "methemoglobinemia." Don't worry we won't be having a test. Methemoglobinemia is just a fancy word for suffocation. NO2 has O2 (oxygen molecules) in it. Hemoglobin love O2. Now if there is too much NO2 it will fill up the hemoglobin with useless gasses, and if the fish doesn't get clean water right away it may suffocate. Prolonged exposure to low concentrations of nitrite can cause irreversible damage to a fish's organs. They can even get brain damage from a lack of oxygen! Some tell tale signs of methemoglobinemia are rapid breathing, erratic swimming behavior, and gasping air at the surface of the water. Fortunately there is a type of bacteria that uses NO2 to make energy, called nitrobacter. The byproduct of this process is NO3- (Nitrate). Nitrate is much less poisonous to fishes. In the average fish only aquarium the only way to get rid of nitrate is thru water changes, and should be maintained at less than 15 mg/L. Again, both nitrite and nitrate test kits are available at your local aquarium store.

2NO2 + O2 = 2NO3- + energy

The following is a graph (Figure 1) showing the natural "cycle" of an aquarium. The "zero day" is when the first fish or nitrogen sources are added to the aquarium. Note the peaks and drops in ammonia and nitrite. In this sample case a peak of ammonia is shown. Nitrosomonas then establish and oxidize the ammonia in to nitrite. The nitrite then peaks as the ammonia fades to zero. Nitrobacter then begins to multiply and lower the concentration of nitrite. Nitrate increases in a linear manner, and must be removed by water changes if sufficient numbers of denitrifying or reducing bacteria are not present.

Denitrifying or reducing bacteria are not present in most fish only aquariums, and they do not exist in abundance in the reef. These bacteria however even in low numbers can prove to be somewhat beneficial. After your aerobic bacteria have done their job the nitrate begins to build up. You can take out large quantities by doing water changes. Realistically we cannot remove all of the nitrates like this. For example we have a new 50 gallon reef tank with 10ppm (mg/L) of NO3-. This is just a little too high to add corals. If we remove 25 gallons and replace it with newly mixed saltwater it will cut our nitrates in half. We will then have 5ppm. Another half change of water would only bring the tank down to 2.5ppm, and another to 1.25ppm. So how do we keep them this low without changing all that water? We need to provide spaces for anaerobic bacteria. In a reef tank live rock is the best place to start. Live rock is simply the rock that composes coral reefs. Live rocks are not live corals, but are composed of dead coral and mollusk skeletons. The outer layer of the live rock houses aerobic bacteria. These are the bacteria that oxidize ammonia to nitrate. As water passes slowly thru the porous rock these bacteria use up all the oxygen. By the time the water enters the inner portion of the rocks there is no oxygen left. This is an anoxic zone. In this zone several different types of bacteria reside including, but not limited to: Denitrobacillus, Micrococcus, Thiobacillus, Pseudomonas, and Sulfomonas. These bacteria reduce NO3- to N2. The free nitrogen gas then dissolves right out of your aquarium and into the atmosphere. Back to top
 
 
Reverse Osmosis Water Purification

Reverse osmosis is the opposite of osmosis. Osmosis is the movement of water across a membrane in order to achieve an equilibrium on both sides of the surface. Reverse osmosis is the movement of water across a membrane in order to form a concentrate, in this case called "waste" water. R.O. does not happen naturally. A lot of energy is used in the form of water pressure. The entire R.O. unit is composed of three parts: the sediment filter, the carbon matrix and the R.O. membrane. Water enters the unit via the tap at between 40 and 60 psi (pounds per square inch) - this is the necessary operating pressure. If you tap does not create that kind of pressure, you can add a booster pump that will create the pressure of between 50 and 100+ psi. Make sure the booster pump output in gallons per pound matches the output of the R.O. filter. When the water enters the unit, it first will pass thorough a sediment filter to remove larger particles like dirt down to about one micron in diameter. The water will then pass through a carbon matrix which will move the DOC (Dissolved Organic Carbon) and solid particles down to .5 micron in diameter. The carbon matrix will also remove chlorine and chlomine. Chlorine will damage a R.O. membrane.

Pictured here is a commercial R.O. unit with a booster pump. It is a Titan 500 and it produces 500 gallons+ of product water per day. The upper gauge shows the outlet pressure of the waste line. This unit allows for adjustment of the wasteline flow by using the valve below the top pressure gauge. The lower left gauge shows the input pressure for the sediment cartridge and carbon matrix. The lower right gauge shows the output pressure of the sediment cartidge and carbon matrix. By monitoring the pressure diffrential of the two gauges the user can determine when the cartidges become clogged. Generally I will label all three cartidges with the date they were replaced to make sure they are replaced at the appropriate times.
 

R.O. membranes are very sensitive, so make sure that the carbon matrix and sediment filter are replaced every two to three months. Finally, the clean (drinkable) water enters the R.O. membrane, At this point, the only things that need to be removed from the water are at the atomic level. The water will pass over the R.O. membrane under extreme pressure. The output has a restrictor valve on it to regulate pressure on the R.O. membrane. You will not see the restrictor valve unless you remove the waste tube Only water molecules are allowed to pass through the membrane and enter the product line. The majority of the water that enters the RO unit is waste and must be disposed of. Only 1/3 to 1/4 of the volume of water that passes through the filter is useable product water. Remember, these units only produce about 24 to 100 gallons per day or more if you buy a commercial unit, so the product line will run very slowly. When purchasing a R.O., be sure to look for one with clear sediment and carbon canisters so you can monitor them visually. Also, make sure you purchase a TFC (Thin Film Composite) membrane. Cellulose Triacitate (CTA) membranes are paper and don't work quite as well. They tend to decompose very quickly and leach into the water. For this reason, you should avoid it. You can purchase an RO unit at a commercial hardware store, make sure they say TFC and the cartridges are readily available. The membrane will need to be replaced every six to twelve months. A total dissolved solids (TDS) meter can be used to measure its efficiency.

A TDS reading over 15 ppm would indicate the need to replace the membrane. Flush kits can be purchased to help blast water over the membrane to clean it off. These are highly recommended. If you have a small reef aquarium, you may be lucky to find a local aquarium shop that sells R.O. filtered water. You can purchase a few large drinking water containers with screw tops to bring the water home with you. I recommend purchasing a R.O. filter if you have a larger aquarium. It will make your life easier. Back to top
 
 
De-Ionization Water Purification
De-Ionization (DI) is what it sounds like. The filter is designed to remove ions from the water. The first two stages in the DI process are the same as RO. It incorporates the carbon matrix and the sediment filter to remove dirt and chlorine. Then, the DI resin will remove the ions from the water by using a (-) force to attract the (+) ions to itself. The cartridge is then discarded when it becomes discolored. No water is wasted in the deionization process, but generally, cartridges last long enough only to make a couple thousand gallons. Another benefit to DI is the speed at which it processes the water. Then end cost per gallon is much higher than RO due to the frequency of cartridge replacement. Back to top
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