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Thread: Low ORP in fresh mixed salt water, why?

  1. #1
    BRS moderator MikeG's Avatar
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    Default Low ORP in fresh mixed salt water, why?

    Why does my fresh mixed salt water have a really low ORP? My tank runns at about 400. When I add fresh saltwater to the tank, it drops to about 270? Is it because of low oxygen content in the freah mixed water since it is not airated? It is mixed in a closed barrel, but the pump does agitate the surface. Seems odd that the balance of oxidizing agents and reducing agents would be that much different in the tank than the fresh salt water. Maybe I should try airating it for a while and see if that brings it up.

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  2. #2

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    i think your on to something there with airating the water first. just like ph in freshly mixed salt water. the non airated batch will have a lower ph. during this process you also introduce co2 wich mixed with o2 will bring up your orp or at least thats my opinion orp is oxidizing redox or reduction potential right?

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    I have noticed that as well Mike. Even if I airate the fresh batch with an airstone for a full day, the ORP of freshly mixed saltwater is WAY lower than my tank water.

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    Senior Toad Licker naturebatslast's Avatar
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    Quote Originally Posted by reefinghabit View Post
    i think your on to something there with airating the water first. just like ph in freshly mixed salt water. the non airated batch will have a lower ph. during this process you also introduce co2 wich mixed with o2 will bring up your orp or at least thats my opinion orp is oxidizing redox or reduction potential right?
    I think I understand what your saying, but, puctuation, capitalization and spelling would help your posts greatly.

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    BRS moderator MikeG's Avatar
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    My only other thought besides the oxygen saturation of the water was the bacterial colonization in the tank that is not present in fresh mixed water.

    Mark, nice to know it happens for you too.

  6. #6

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    no insulting remarks please
    Last edited by NateHanson; 08-02-2007 at 01:35 PM.

  7. #7

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    Fresh mixed SW has a ORP of about 235mv, always has, always will. So, your ORp will fall after water change, not to mention from "stirring" up stuff in the aquarium. If you have a stable 380-400mv, it will return to those numbers quicky after a water change.

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    too many gadgets to fail Aquaman_68's Avatar
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    remarks about previous insulting post removed.
    Last edited by NateHanson; 08-02-2007 at 01:38 PM.

  9. #9
    too many gadgets to fail Aquaman_68's Avatar
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    Quote Originally Posted by MikeG View Post
    My only other thought besides the oxygen saturation of the water was the bacterial colonization in the tank that is not present in fresh mixed water.

    Mark, nice to know it happens for you too.
    It happens to everyone Mike.......If you try to aerate it all you do is force c02 into it. (& that will lower it more) As most homes are high in c02 due to being closed up & the amount of air we use up. I found way back in the early days of my reefing. (pre DI) orp levels were lower after doing a water change but never as low as they are when using RO/DI water as opposed to using just RO water for mixing up ASW. It gradually comes back up after 3 or 4 days usually at the most. They key is that it is consistant everytime you do a WC. (or relatively close)

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