Oxygen in a planted tank.

Discussion in 'Planted Tank Equipment' started by STRiDER, Nov 14, 2006.

  1. STRiDER
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    STRiDER Noob

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    I read in a book that with a planted tank you must minimise surface agitation to reduce oxygen content in the water.

    Is this true?

    1. Does this mean I must lower the outflow pipe of my filter to be 5cm below the water or must I rather use a spraybar? (Filter rated at 1100 l/hr)

    2. What about my powerhead pumping bubbles through a venturi into the tank, do I still need this? (Powerhead is also rated at 1100 l/hr).
     
  2. Cameron
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    Cameron Green fingers

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    Yes it's true, it keeps CO2 in solution longer, thus giving your plants the CO2 they need.
     
  3. Anonymous
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    Surface agitation increase gaseous exchange. So it's not the only gas content that you reduce/change in the water.

    1. Yes, if you can lower your outflow it will be better. Spraybars just dispears the current a little bit.

    2. Yeah, I would take off the venturi. It really serves no purpose.
     
  4. STRiDER
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    If I minimise surface agitation and remove the air bubbles from the powerhead, how will the fish survive.
    In other words where do they get oxygen from?

    (I know the plants will create oxygen, but this is only during the day)
     
  5. Cameron
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    Cameron Green fingers

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    Unless you're overstocked the oxygen in the water is enough to carry them through the night.
     
  6. Galibore
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    Can someone correct me if I'm wrong please, it's been a while.... (I'm sure Cameron would jump in here again)

    I read somewhere, (will try and find the article again) that oxygen and CO2 does not "compete". In other words, the one does not displace the other. So you can have high saturations of both at the same time.

    So Strider, if this is correct, then it's not so much about reducing oxygen, but maximizing CO2.

    Cheers
     
  7. Cameron
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    Cameron Green fingers

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    Galibore, I'm not exactly sure how it works but i too have read articles that state similar to what you are saying.

    Let me see if I can dig up some reference material.
     
  8. STRiDER
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    Am I then correct in saying that surface agitation must be minimised to prevent CO2 from "escaping" from the water.


    EDIT : The reference book I'm using (The Perfect Aquarium : Jeremy Gay) also states that aeration devices and surface agitation should be minimised to prevent "oxidation of nutrients". Also to prevent this they suggest not filtering the water more than 3 times per hour.
     
  9. R.C.
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    Correct, yes. 8)
     
  10. Galibore
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    That is how I understand it.

    I don't really know what "Oxydation of nutrients" is, or why it is bad.
     
  11. STRiDER
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    I also have no idea - but they talk about this under the "growing plants" section. So it must have something to do with plant nutrients ???
     
  12. Andre
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    Andre Green fingers

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    Hi Strider

    I have actually been told exactly the opposite. You want optimal ORP (oxygen reduction potential - it is the same as redox) levels in your aquarium. Your biological filtration and other things (including some medications) will lower your ORP.

    Big water changes will help boost your ORP, also, adding some airstones will also help.

    If you want to learn more about ORP go to this awesome thread on finarama.

    http://www.finarama.com/forum/viewtopic.php?t=466
     
  13. Galibore
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    Mmm... this is turning out to be a very interesting topic.
     
  14. STRiDER
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    ??? ??? ??? ??? ??? ??? ???

    I should never have brought this up :scratch:

    Now I'm more confused than ever...

    Clearly Redox (Dissolved Oxygen) is good for fish.

    However, is it good for plants.

    If you get Dissolved oxygen in the water, do you then also get "normal" (undissolved) oxygen in the water?

    :scratch:
     
  15. Andre
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    Andre Green fingers

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    Hi Strider

    Redox is not a measure of Dissolved Oxygen - it is a measure of the oxygen reduction potential of the water.   I am guessing that the book refers to the fact that some of the nutrients might be oxydised and be unusable to the plants.   For instance Iron would be oxydised and form rust.    To counter this the nutrients need to be chelated which prevents this to a certain degree.

    I am hoping dirk will comment, but here is a quote from him on the aquatek list

     
  16. Andre
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    Andre Green fingers

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    I also forgot to add that plants actually raise the ORP in your tank by photosynthesis as well.
     
  17. Cameron
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  18. Dirk B
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    Hi Guys,

    and now you expect me to try explain how this whole lot works... let me try to simplify things (if this is possible) by listing them in point form:

    1. CO2 will be released from water by aeration or by strong surface agitation and certainly by the venturi. So try to reduce this as far as possible as it nullifies your CO2 fertilization. CO2 fertilization during the day, when plants photosynthesize, causes the plants to produce oxygen, which can be used by the fish. During the night, THIS DOES NOT WORK. So plants will not produce oxygen and unless enough oxygen gets into the water through the surface area, or agitation or aeration, your fish are at risk. If your stocking levels are not too high, you should be OK without aeration or agitation, if they are high you might be in trouble and could have fish dying overnight due to oxygen starvation.

    2. Running CO2 fertilization at night means that the plants cannot utilize it, and it therefore serves no purpose but additionally, and this is very detrimental, it will dissolve in the water, react with the water and form carbonic acid which causes the pH to drop, and can be lethal for fish. pH regulators for CO2 canisters (soda stream bottles etc) stop the release of CO2 during the night because as the pH drops the regulator switches off the CO2 supply. Ever so often I see mention of CO2 use for plant feeding with soda stream bottles WITHOUT regulators, and all I can say is: THIS IS LETHAL FOR YOUR FISH during the night!

    2. Aeration obviously introduces oxygen to the water, which is good for your fish. At night the fish still need oxygen, but the PLANTS ACTUALLY ALSO NEED OXYGEN! So, if you have lots of plants and fish, the oxygen levels can actually go quite low during the night. As Cameron has indicated, the general opinion is that if you do not have too high stocking levels, you should be OK as regards oxygen levels, but no one has done any measurements on the dissolved oxygen in their tanks and I would actually like to see what the actual levels are. Potentially, they could go down so low that they are a risk for your fish at night. If your fish load is high, I would consider aerating at night, and if your plants are producing enough oxygen during the day as a result of CO2 fertilization, then switch off the aeration during the day. Basically, the only way to answer these questions with regard to a specific tank is to do oxygen measurements.

    3. Then, ORD, or oxidative reduction potential. As the name indicates, this is in some ways related to aeration and oxygen supply, just simply because of the name. But, it is a vastly different concept. In any biological environment, such as an aquarium, the fish and plants are producing waste. This waste can be ammonia released via the gills of the fish into the water, droppings released by the fish, plant parts that are dying, bacteria in the filter that are dying etc. Once these substances are produced, or the plant bits and bacteria are dead, they tend to need oxygen to decay fully. All of these processes require oxygen. Ammonia (chemical formula: NH3) is converted to nitrate (NO4), where does the oxygen come from? From the available oxygen in the tank. Organic waste is also broken down into compounds and this requires oxygen. ORD, is the actual capacity of your aquarium to be able to perform these processes quickly using oxygen. How? Through a good filter with a high biological filtration capacity, in other words, lots of bacteria that convert ammonia to nitrate as fast as possible. If ammonia accumulates in the water, it is lethal for the fish, so a high ORD is essential for keeping fish healthy. If you have a lot of rotten plants in a tank for example, they will be broken down by bacteria (like a compost heap) but this also requires oxygen to break them down. If your tank has too little ORD, it will not have the capacity to break the plants down fast enough and will lead to toxic by products being formed. Throughout all of these processes oxygen will be used, and if at any point there is too little oxygen in the tank, they can accumulate and this will be to the detriment of your fish AND PLANTS. A new aquarium that is not "matured" as we like to call it, has far too little ORD as a result of which your fish are at risk.

    4. In practical terms, what must I do to maintain a good ORD? Run a strong filter with sufficient surface area, by that I mean enough Siporax, bioballs, filter wool, sponge etc etc so that ammonia is never a problem. Do not let large amounts of uneaten food accumulate as this liberates lots of ammonia and puts the bacteria in the filter under strain. Do not let any rotten plants accumulate. Clean your filter ever so often, not too often or else you remove too many beneficial bacteria, but not to infrequently so that the bacteria die off in the filter because it runs too slowly. That should keep your ORD happy.

    This explanation has now taken me an hour, if you have more questions, please ask...

    Kind regards,

    Dirk
     
  19. Andre
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    Andre Green fingers

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    Thanks Dirk

    As you an efficient bio filter needs enough oxygen to perform optimally, but in effect it lowers your ORD/ORP. This is why trickle filters work so well. Most of the oxygen is taken from the atmosphere, which does not put additional strain on the ORD in the tank.
     
  20. Tucker
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    Hi STRiDER,
    Getting back to your original Q...
    Just wanted to point out that I use CO2 fertilization & I've experienced that
    minimizing surface agitation will help KEEP CO2 in the water longer & as a
    result your plants will produce enough O2 to keep your fish happy :) (provided you have enough plants & nutrients).

    Its not so much a case of minimizing surface agitation to reduce O2 in the water, as it is for decreasing the rate at which CO2 dissipates or escapes.

    As a precaution, always monitor your fish for signs of low O2 and pH shock when adjusting your system.

    HTH
     

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