February Article - BcOD
What is BOD or BCOD? BCOD is BIOCHEMICAL OXYGEN DEMAND. Now that says a lot does it not? Nope!

What is normally referred to as BOD is Biochemical (or biological) oxygen demand. It is a measure of the content of ORGANIC MATTER in water and wastes. It is the amount of oxygen (mg of O2 per cubic decimeter of water) when a sample containing a known mass of oxygen in solution is kept at 20 O C for 5 days. The oxygen is consumed by microorganisms that feed on the organic matter in the sample.

Is BOD so important to the Hobbyist? Yes it is! Why? Because BOD has a direct correlation on how your tank is functioning. I shall now explain how and why.

Many people in this hobby have conflicting view points on how they maintain their tank. As there are people, there will be about the same amount of "experts" that ‘KNOW" about this or that. But when confronted by basic chemistry, they usually fall to the way side, or leap upon the Nitrogen cycle as a spring board.

There are people who change their water weekly and there are people who never change their water, "because they want to maintain the "Natural Balance" in their aquarium." When asked what they mean about the "Natural Balance", they refer to the ocean and attempt to make their 55 or 250 gallon aquarium in the same slot.

Granted, it is everyone's desire to have an Ocean Ecosystem, but many people fail in their knowledge when they say, "I have low or no Ammonia, Nitrite, and Nitrates!" Little do they realize, there are a great many other factors that are directly affecting their organisms. One of the MAIN factors is BOD.

Every time any of your living organisms eat and excrete waste, they are contributing to the buildup of BOD.

People complain of micro algae (slime algae) and Macro Algae (Hair algae). Invariably, they will always point to PHOSPHATES at the leading cause of Hair or other algae. What they don't realize like BOD, there are other factors that contribute to hair algae.

In the 18th Century, a German Chemist, found that in order for a plant to grow, it needed THREE basic chemicals. The THREE basic Chemicals are, Nitrogen, Phosphate, and Potash. If ANY ONE of these three were removed, the plant would quit functioning, and die. In the aquarium we must have all THREE of these ORGANIC compounds, for our plants to live, flourish, and generally over run the tank. Carbon is also needed, but for plants, I am speaking of the three MAIN chemicals.

As in any river, lake or stream, the normal amount of these compounds, contributes to the well being of the plant and animal life found there. Without these compounds, life would cease to be on this earth. But when we have an over abundance of these chemicals, lakes, and all water ways become clogged with unruly algae. So it is with your tank.

If you did not have these three chemicals in your tank, then you would not have the Nitrogen Cycle. Your fish would die. And soon you would be hunting aardvarks that roam within your city boundaries as a hobby.

As mentioned before, every time your organisms place waste in your water, you start to build up your bank account of BOD. So what happens when you have a high BOD?

People that have high Nitrates, Phosphates, etc., will tell me, they have done many water changes without any effect. I always ask them if they vacuumed their gravel, and under the rocks, and they say, no. But they say, they changed half the water, and still they have high readings on their test kits. I shall explain how this occurs.

The BOD that is trapped in your gravel, under your rocks and in your filter, you normally call dirt. So we shall use that same word in our explanation.

The dirt is not totally decomposed. This same dirt contains all the elements such as nitrogen waste, phosphates, potash, and a myriad of other compounds that keep a tank healthy. This same dirt is a bank. It keeps all of your wastes, intact, and in balance with the surrounding water.

If your water has 100 mg/L ( milligrams per liter, which is the correct way of stating compounds in your water) then your dirt bank normally has the same amount. The reason the dirt bank does not release its 100 mg/L into the water, is because the water and the dirt bank has the same equation with each other.

If one does a 100 percent water change without cleaning the gravel at the same time, they will notice in a few days their readings will bounce to about 50 mg/L. The reason, the new water did not contain these compounds, so your dirt bank is now releasing them into the water until, these compounds reach equilibrium. In the mean time, your organisms are adding to this pollution.

While you do a water change, you vacuum the gravel, under the rocks, and the rocks themselves, you are riding your self not only of the amount of compounds in your water, BUT ALSO THE STORED COMPOUNDS IN YOUR DIRT BANK! Water changes should be every other week (about 25% removed) and no longer than one month.

IF you vacuum your gravel, etc.,, you will find your readings dropping far lower with each water change. This will help balance your tank far better than adding any chemicals to do the same job. If you have access to natural sea water, you will even further enhance your tank and the long life of your organism.

One thing you must NEVER do is use a canister filter to trap the dirt as you vacuum your sand, and at the same time return the same water back to the tank. If you do this, your BOD will sky rocket, because you are mechanically increasing the BOD in your water

Always discharge your water into a bucket or use a hose. Lugging buckets can be a real pain some times. How I do my water changes are very simple. I bought a clear tube from a Local Fish Shop for vacuuming purposes. I noted the hose that went with it was very thin and tended to kink. I went to Home Depot and bought a hose that would slip over the discharge end. The hose also has nylon to reinforce it, so it will not kink. Instead of three feet, I bought 10 feet. I used super glue to fasten it on the top of the tube, so it would not fall off, or break my vacuum.

I also purchased a female plastic hose fitting. I put this fitting on the other end of the hose. The hose was 5/8 inside diameter. I cleaned my garden hose off with a damp rag, and took it into the house. I made doubly sure, the fittings on the hose were good, and not bent. I unrolled it, and put one end in the shower, or tub, and the other end, I screwed on the hose with the vacuum tube.

I started my vacuum, by kinking the vacuum hose while filling up the other end, by dipping and holding the tube up, to allow the air to escape. Then I put the tube in the aquarium and un-kink the hose.

I stick the tube into the gravel. It will always pick up the gravel. I allow this to happen, until the plug of sand is about half way up the tube. I kink the hose for a moment, and the sand drops. But the dirt is suspended for a moment in the tube. I release the hose and the dirt is sucked out.

I clean the gravel in this manner starting from one end and work my way to the other end. If the tank was really dirty, I will have to wait a week and start where I left off. When I am done, I simply roll the hose, starting from the tank to the bath tub. The water is pushed out into the tub, and I have no water on the deck.

Soon though, I will have clean gravel and a very low BOD. This means:

1) Less Fish death and diseases.

2) Less Fish diseases.

3) More apt to reproduce.

One important thing I should mention. If you use a little Right Now Bacteria, after your water change, this will preclude any ammonia/nitrite spikes. Also, this same bacteria will chow down on the BOD your fish are making. Thus, you will have less BOD mass to deal with each time.

February, 2001
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