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  1. #1
    Senior Member tang_man_montreal's Avatar
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    Wonderful explanation of ORP.

    I found this wonderful explanation of ORP in layman's terms... thought I'd share it with everyone...



    To explain a little further, ORP is a potential energy. In other words, ORP is a value that determines the ability of your water "to do work."

    True ORP is measured in negative millivolts. However, most monitors record the value as a positive value to simplify the display. Therefore, a normal ORP value of "-360mv" will be displayed as "360".

    In chemical terminology, electrons represent a negative charge. Electrons can be thought of as a source of energy. ORP measures this flow of energy.

    Here are two examples of the importance of monitoring ORP:

    1. This morning my ORP was at -360mv. I added a calcium supplement to the water. According to a chemistry periodic table, calcium is Ca2+. That means it is a positive cation with a plus 2 charge. Therefore, you would expect the ORP to become more positive in value. This is precisely what occurred in my tank. 20 minutes after adding the supplement, my ORP was -320mv. An overall change of +40mv. This is a good example of inorganic changes in the water column. Adding other cation supplements to your water has a similar effect.
    Now, what is cool about understanding ORP is that the value will return to the norm of -360mv. What determines the speed at which the value returns to normal is the rate of converting Ca2+ ion into the tissues of stony corals and other animals, to a much smaller degree. Remember, fish require calcium to build bones too. So, a tank with lots of stony coral will theoretically use up the calcium ions much quicker than a tank with less stony corals.

    2. What do you think occurs after the death of an animal? The organic materials within the tissues become recycled. This process is known as catabolism, the breakdown of organic material. So, how does ORP fit into this scenario? Well, the process of catabolism requires energy. So, our potential energy as stored in ORP will begin to do work. The value of -360mv will become more positive. In cases of fish death, it is common to see a value change +100mv. So, your ORP will now be observed at -260mv. This is an indication to the aquarist that something is decaying. If you cannot find and remove the fish, than it will take longer for the ORP value to return to normal.
    Now, as you can image, the quality of your system "to do work" has been diminished during this decay process. This means two things. One, the anabolic processes (building organic tissue), like the continued growth of corals will be severely retarded during this lowered ORP phase. Two, if another animal death were to occur, this will further lower the ORP value and can cause serious damage to animals as well as enhancing the opportunity for parasitic infections and algal growth. The bottom line is to determine the cause of falling ORP, and in the case of fish death, remove it ASAP.

    Controversially, some aquarists prefer to allow dying animals to decay in their tank, "allowing nature to take its course." I strongly discourage this practice. In the ocean, ORP values remain nearly constant all the time due to the huge water turnover rate and vast size. However, in a closed environment, as seen in example two above, the consequences of catabolic processes can cause more problems than one is willing to negotiate with.

    Therefore, ORP is a valuable tool that gives the aquarist the ability to "see" physiological changes as they are taking place.

    Remember, simply said, ORP is the ability to do work. The higher the value, the better. When ORP values dip, one should investigate the cause and alleviate the problem. Two likely causes are animal death and the addition of ionic supplements.
    I am Homer of BORG... Prepare to be..OOOO!! DONUT!!!!!!

  2. #2
    ijo
    ijo is offline
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    very good article TM!!! karma to you :thumb:

  3. #3
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    Yes .. good article because a lot of hobbyist don't understand ORP. I dosed my 100 gallon fish only tank Sunday with Green X and the ORP immediately dropped 23 points. It did not return to the normal level for many hours. I think these meters are very handy for monitoring water conditions .. I live by mine ... and so do my critters :-)

  4. #4
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    this thread should be in the file section so it would be easy to find it
    25g Reef

  5. #5
    Senior Member MalHavoc's Avatar
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    Randy Holmes-Farley has written a great article on ORP for this month's reef keeping magazine:

    http://reefkeeping.com/issues/2003-1...ture/index.htm
    Jason Nugent
    http://malhavoc.homeunix.com/
    ReefCentral Admin

    180 gallon Oceanic with Lifereef Sump, 33 gallon with VHO, 20 gallon frag tank with MH

  6. #6
    Senior Member tang_man_montreal's Avatar
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    Thanks for the link!
    I'm gonna have to call in sick for a week to read through that immense article though!
    I am Homer of BORG... Prepare to be..OOOO!! DONUT!!!!!!

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