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|April 2001 / Article - AIR, OXYGEN AND CARBON DIOXIDE
In the aquarium field, many tanks are made to run silent, run deep. This is fine, if the manufacturers and hobbyists are thinking like U-Boot Commanders, rather then the welfare of their fish and invertebrates. This is not to discredit the manufactures of the trade nor the people within it, (for I am one of them also) but to simply show, many of the filters are dynamically opposed to good fish keeping.
In my years with Fish verses the Environmental industry, I have found, people in the Environmental area are more open to new ideas and are willing to try different things as long as there is a solid science base for it. Whereby, the Fish industry, if a person makes a new design and has some success, within a month, the clones are on the market. These clone makers tout unfounded claims without a real world test to back up their assumptions. They sell what it appears like, rather than what it actually does. There is no performance data, just flash and good packaging.
A case in point was the fluidized bed filter. This filter first appeared in 1891. Its primary use was to REVERSE FLOW human waste, and at the same time fractionate waste without costly electric sewage grinders. This idea was well and good, but fail in practical use because of many things.
1. The waste from the city also contained many items that were not broken apart with sand. This included wood, metal, cloth, etc.
2. The constant adjustment of the flow on the bed had to be regulated manually. Too much flow, caused the sand to over flow and drain to the sea. Too little flow caused channeling in the sand, thus the filter could not perform its job adequately. When the sand became loaded with waste, they needed to flush it away and start again.
3. The constant rubbing (grinding) of the particles against each other, did not allow sufficient time for a total population of bacteria to evolve. Since the NORMAL (Not Right Now! Bacteria) Reproduction Cycle takes about 29.7 minutes for a division of cells, many of the cells outside in the fluid media, were destroyed. This allows a sub level of organisms to perform.
4. The surface area of the media was maximum 390 m2/gram. No matter how tiny the sand appeared to the naked eye, using the Nitrogen BET Test to determine true surface area, the surface area never exceeded 390 m2/gram. Some times, the sand ranged as low as 150 m2/gram.
5. Because the system was not under pressure, the amount of total dissolved oxygen the water could carry, was already set, by the temp, pH and elevation of the waste treatment plant.
Yet, none of these items were discussed by the Aquarium Trade. Point of fact, some claims were actually reverse of scientific findings. One point was touted by many people. They claimed, the constant rubbing of the sand against itself, allowed the old cells to sluff off and new ones to appear. Since the cells were constantly in motion, and in replication rate was every 29.7 minutes, the only cells that survived to any great extent, were ones deep within the crevices of the sand. As they split, their asexual "offspring" were lucky not to be destroyed by the sandpaper effect of the media.
This is not saying fluidized beds do not work, indeed they do! But NOT to the extent some people claim. In the Environmental business, we still use fluidized beds, but only with heavy hydrocarbons (tar like substances), or organic materials we wish to break down. The tar floats through these beds and is reduced in both volume and toxicity by the organisms and the sand. It is not considered to be most efficient manner to break down this type of waste. Some times fluidized beds are the only method available, due to the remote job site or the compounds needed to be reduced.
What does this have to do with Oxygen in your aquarium? A lot!
Some manufactures make their filters to be "noiseless". They do this to please the ear of their customers, because they believe (and rightly so) people do not want to hear rushing water in their tanks. Besides, this also leads to splatter, which can cause build up of salt creep or calcium deposits. So most of them have a "silent water fall" or instruct their customers, (in the case of canister filters or power heads) to place the returning water UNDER THE WATER!
They assume incorrectly, the movement of the water is sufficient to aerate their customers aquarium. This could not be farther from the truth. In fact, it sometimes leads to gas subjection of their customers fish and inverts.
To understand better what I am speaking about, let us take one Gallon of water. This water for the sake of instruction will be kept at 76 degrees F, the pH is 8.4 and the water density is 1.025. This tank is at sea level. Now if you raise any of these parameters, the Oxygen carrying capacity is reduced. Simply means, the higher the temp, pH or density, the water loses its ability to carry more oxygen. This is one reason it is so important to monitor these areas.
If you have a density of 1.025, the temp is 76 degrees F, and the pH is 8.4, then your reading of all salts AND other minerals is known as DENSITY, NOT salinity. If you elevate the temp to 80 degrees F, without adding any more salt mix, your density will drop because the volume of water is slightly greater (expansion). Likewise, if you cool this same gallon of water, your density of TDS (Total Dissolved Solids) will rise. (contraction)
All bodies of water contain gas. Gas in this instance means Carbon Dioxide, Oxygen, Nitrogen, Argon, etc. The water in your aquarium does not care WHAT gas is present, but only the REQUIRED AMOUNT of gas according to the above parameters are met. As you learned in school, nature does not care for a vacuum. Your aquarium tank is no exception. If one gas is in abundance (dissolved) than the water is saturated with that gas AND NO OTHER GAS CAN DISPLACE IT as long as that body of water remains static!
You will notice sometimes a very mal odor rising from a tank. This could be it is newly set up, a lot of dead (uncured) - Live Rock in your system, your fish are not as lively as they should be, or, the tank is not cycling as it should. All of these are directly attributed to a low Dissolved Oxygen content in your tank, assuming correctly, your fish are in grand health.
Aeration of organisms in nutrient liquid may reasonably be expected to do three things.
1. Supply the physiological oxygen requirements of the living organisms. It can be either fish, inverts, or protozoa (bacteria, etc)
2. "Scrub" out volatile metabolic waste products
3. Provide a measure of agitation throughout the suspension.
Of these, only the oxygen supply has received much careful attention, and certainly is of very great importance. To better understand the extent of our knowledge, let us examine each of these in some detail.
Cellular oxidation of organic matter can proceed either in the present or absence of molecular oxygen. If air is present, (aerobic condition), the oxidation process is called respiration. If air is not present, (anaerobic condition), fermentation is ensuing.
Studies of these cellular processes, while lacking much in detail, have made the general, fairly clear. Substrate oxidation is apparently a step wise process. This involves many enzymes, each operating in a cyclical manner to give a smooth reaction system. Many intermediate compounds are formed and rapidly degraded. Therefore, the lives of these molecules are very short and their concentrations are very low.
Such mechanisms permits a gradual release of the energy available in the substrate and its efficient transfer to synthetic processes in the cell. Is it true, because the reactions are all operating near their equilibrium point. As mentioned above, the amount of dissolved gasses in any given body of water.
In the aquarium process, molecular oxygen is available, and we may confine these remarks to a consideration fo respiration. Fermentation may occur if the oxygen supply is diminished in the substrate, and oxygen is displaced with other gasses. This is undesirable.
Such conditions usually gives ways to poor clarification, mal odors, lower pH, displacement of remaining oxygen and destruction of the detritus in the aquarium. Sufficient oxygen (as air), must be supplied to keep the oxidative mechanisms as FULLY AS RESPIRATORY AS POSSIBLE! This is one of the MAJOR requirements for DESIGN and OPERATION of the aeration system in your aquarium or hatchery.
OXYGEN DEMAND AND SUPPLY
To proceed logically, it is desirable to know, within reasonable limits the oxygen demands of organisms normally present in biological aquarium systems. The effects of various physical and chemical variables on these oxygen requirements must also be examined.
Oxygen demands in any system, are normally reported in terms of specific uptake rates. While a variety of expressions, usually volumetric ones like Qo2 [volumes O2/(hr) (mass of dry tissue)] are used, the term kr will be adopted for this discussion. This is a mass rate, defined as follows:
mg O2 utilizedkr ------------------------------------
(hr) (grams dry tissue)
It is very difficult to determine the amount of respiring tissue (fish, inverts, bacteria), and hence the denominator of this expression. In an aquariums BcOD, for example, there is no ready way to separate some of the organisms (bacteria) from the solids adsorbed and occluded during clarification. A modified uptake rate, rR, may then be employed with some accurate degree.
mg O2 utilizedrR = ------------------------------
(hr) (liters of suspension)
These two rates may be related when the active tissue concentration is known:
rR = kR --------
s = ppm dry tissue of all the organisms in the system.
By now, you are scratching your head and saying to yourself, WHAT DOES THIS HAVE TO DO WITH ME???
Some people in the hobby, have this ornate desire to convert all functions to a mathematical equation. This is for their benefit.
HOW DO I ACCOMPLISH THIS FEAT?
To accomplish allowing more oxygen in to your tank or system is very easy.
If you have a canister filter, or a hose from your wet dry, simply place the discharge (water returning to the tank) slightly ABOVE the water line instead of under the waters surface. Jet the water across the surface of the tank.
If you have a water fall type of filter, place something in the waters path so the water is a broken flow rather than a smooth flow. Much like rocks in a water fall.
If nothing else is available, buy an excellent air pump and allow the air to "BOIL YOUR WATER!"
The reason for this is very simple. Bacteria and your organisms (fish and inverts) respired. They use Oxygen and expel Carbon Dioxide. Your water does not care if Carbon Dioxide or Oxygen is present. The return tube splashes the water across the surface, like small swells and waves in the ocean. At no time, is the water in the ocean still. There always is motion. This area, the top of the water is where most of the gas exchange occurs.
The Carbon Dioxide is driven off, and expelled from the aquarium BEFORE IT IS DISSOLVED INTO SOLUTION! Since a vacuum of gasses now occurs in your tank water, Oxygen (air) fills that vacuum.
This IS very important when using Right Now! Bacteria in your tank. Since these organisms are highly aerobic and instill a Different Totally Aerobic Nitrogen Cycle in your system, it is very essential you supply them with this life giving gas. Your Nitrogen and Phosphates will be less than you normally expect using the Right Now Bacteria.
With a system that incorporates HIGH FLOW and LOW PRESSURE, your aquarium pets will thrive and thrive. One such shop is Aquatic Life, Inc , 1525 South East Luckhardt Street, Stewart, Florida. Carl and Nancy have built their entire shop around the Hiatt Life Support System. Not only do their fish eat when they are received, BUT the fish liven and brighten up when put in their system.
If you are in their area, give them a call and drop into their shop. You will be glad you made the trip. They are the largest fish shop in the area.
So in closing, give your fish and inverts more oxygen (air) than what you believe is necessary. You will find, maintaining your tank, will be a whole lot easier.
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