Redox - Why don't we measure it?

Discussion in 'Water Chemistry' started by jameson_uk, 8 Jan 2019.

  1. jameson_uk

    jameson_uk Member

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    I have recently come across a few mentions of redox and the impact on fish health.

    ORP measurements seem prevalent with reef keepers but there was a suggestion that it was equally useful for freshwater. (exactly how was unclear and I guess this is a bit like TDS and probably more likely to cause confusion than actually help anything?)

    I guess the question I have is whether redox is actually important? This is a proxy for BOD so presumably it would be an indication of a build of of organic waste or overstocking?

    I see that ORP meters are pretty expensive but if they were the same price as pH pens and also accurate would we all be using them?
     
  2. dw1305

    dw1305 Expert

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    Hi all,
    We have a couple of threads that mention <"ORP or REDOX"> values.

    If you look at the situations where people are most interested in them (Reef Tanks, and to a lesser degree Rift Lake Cichlid keepers), it is in alkaline, highly oxidising environments where the higher the ORP values are the better. It is a "black and white" scenario where high ORP values are good, and low ones are bad.

    If you think about <"foam fractionaters or protein scrubbers"> they are physically removing DOC from the water, but you can use chemical options, and I think some shrimp keepers use the <"Söchting Oxydator">, a hydrogen peroxide (H2O2) generator. A substance like Purigen (and the Twinstar Mini/Nano) probably fits in here somewhere as well.
    It is, but we are back to the "shades of grey" argument.

    If you think about a Coral Reef (or the surge zone of Lake Tanganyika), it is a very small specialized part of <"a much larger ecosystem">. In the case of the reef, its survival might depend on the Turtle Grass (Thalassia testudinum) meadows in the lagoon, fringing Mangrove swamps behind the lagoon and the huge volume of nutrient poor ("oligotrophic") open ocean washing over the reef twice a day.

    These areas are performing many of the other functions that produce the stable, low nutrient, low sediment, highly oxygenated conditions that the reef needs. You don't have the luxury of a <"mangrove swamp"> etc. in a normal reef tank, so you have to use other means (deep sand bed, protein skimmer, phosphate/calcium reactor etc.) to retain water quality.

    I like to think of ecosystems as spatial and temporal mosaics, patterns in space and time, that replicate themselves on <"different scales">. If you think about freshwater streams and ponds etc the situation is slightly different, you don't the same spatial separation of the different functions, but they are still occurring. You also have much more terrestrial input of nutrients, dead leaves, sediments etc.

    In a planted freshwater aquarium we help nitrification along by providing a biological filter (which allows us to keep more fish), but other than that we can replicate the natural situation more closely.

    In a tank, with a substrate and plants, you will have different REDOX values:
    • in the deep sediment there will be reducing conditions (negative REDOX potentials)
    • and in the rhizosphere/upper sediment (zones with diurnal REDOX negative/positive fluctuation)
    • and in the tank water (always positive).
    The zones of negative and fluctuating REDOX values will be particularly important in making mineral nutrients available to aquatic plants. The natural REDOX values of streams and ponds will also vary and they would be much higher in a chalk stream (or Lake Tanganyika) than in a black-water peat swamp.

    The only place where I explicitly like a spatial separation between the aerobic and anaerobic processes is in a canister filter, the reason for this is that you have a finite amount of oxygen that enters the canister and you run the risk of ammonia rich, de-oxygenated water, flowing back into the aquarium.

    This is back to <"risk management">, even limited exposure to low oxygen and/or high ammonia is going to kill your fish.

    cheers Darrel
     
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  3. dw1305

    dw1305 Expert

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    Hi all,
    That should have said "an oxygen generator using H2O2 and a catalyst".

    cheers Darrel
     
  4. jameson_uk

    jameson_uk Member

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    I saw a few references to ORP but not whether measuring it was actually helpful or not.

    This wasn't the article I was looking for but as always you never seem to get back to what you were reading . I suspect what I was reading did originate here though

    http://www.americanaquariumproducts.com/AquariumUVSterilization.html

    Which lists one the benefits of good UV as
    Which I can't say I understand. I get you can measure ORP but this seems like words....


    Will the redox of the water always be positive? With a high bio load, dirty tank with unhealthy plants and hard alkaline water could redox not become negative?

    Also can redox (well ORP) be too positive? (The article above talks about oxidative stress)
     
  5. dw1305

    dw1305 Expert

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    Hi all,
    The REDOX values in the water need to be positive, you can get negative values in sewage etc where the COD/BOD may be many times higher than the total amount of oxygen the water could hold (from <"https://www.thewastewaterblog.com/single-post/2016/12/18/ORP">).
    [​IMG]
    Yes, which is why the sellers of ozone generators etc. offer <"a disclaimer about proper use">. Oxidising agents are exactly that, they oxidise organic matter. You could potentially have a "sweet spot" where single celled organisms (particularly prokaryotes) are damaged and eukaryotes undamaged, but as soon as your oxidising agent reaches a higher concentration then damage and death to all living organisms is a guaranteed. One of the ways that UV works in a similar manner, it disrupts the cell membrane.

    Have a look at <"Oxidation-Reduction Potential for water disinfection.... ">
    cheers Darrel
     
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  6. Oldguy

    Oldguy Member

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    Thought about playing around with ORP. Very tempting to use an ozone generator, especially as I have one given to me, but its always best to measure twice and cut once. The reality was, in my view, more trouble than it was worth. There are clear benefits but major snags. Also thought about drip application of H2O2 solution, but again snags out weighted benefits. Topical application is of use. Settled for good biological filtration and lots of plants, a few fish and 'dry salt' fertilization. Good UVC is worth looking at.
     
  7. jaypeecee

    jaypeecee Member

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    Hi Folks,

    I'm very interested in redox/ORP. I am able to measure ORP and have gathered some data from one of my tanks (freshwater). It does appear to be a useful indicator of the state of health of a tank. I was getting readings around +230mV. There is a guy in the US of A called Carl Strohmeyer who has written extensively on this topic. Search the internet and it will take you to some of his articles.

    Edit: I've just noticed that you mention American Aquarium Products which, if I remember rightly, is run by Carl Strohmeyer.

    JPC
     
    Last edited: 1 Feb 2019
    dw1305 likes this.
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