Yoghurt and cycling

Discussion in 'Water Chemistry' started by brumbird, 26 Feb 2014.

  1. dw1305

    dw1305 Expert

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    Hi all,
    Pretty much in terms of biological filtration, if you look on a lot of marine forums they've gone away from wet and dry trickle filters because they are "nitrate factories". All this really means is that because these filters have a huge gas exchange surface, and the filter media remains aerobic, you can deal with a huge bioload.

    All aerobic is definitely a winner for me.

    A lot of discussion on the more expensive filter media relates to them potentially supporting both aerobic and anaerobic within varying sized pores. I can't see any point to this, all it means is that a small increase in your bioload will cause all the filter media to become de-oxygenated, with catastrophic results.

    Have a look at "Greg's Peas" posts in this thread <Alfagrog for reducing Nitrates? | UK Aquatic Plant Society>.

    cheers Darrel
     
  2. brumbird

    brumbird Member

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    OK I've read it all properly now, had to make some notes to keep myself on track :)

    I am glad to have read an explanation for keeping the tank clean and doing water changes - at first I didn't get the link between BOD and nitrification but the last article spelled it out very well.
     
  3. brumbird

    brumbird Member

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    I got everything else but this :) don't worry if you are sick of explaining everything to me, I get it off my toddler (why, why, but why mommy...!)

    I've seen a video about the anaerobic nitrate munching bacteria, can't say it interests me though as I've barely registered nitrates in my tank since I completed the cycle (I know you guys don't like test kits but hear my point) because its a jungle full of elodea frogbit and java fern :)
     
  4. dw1305

    dw1305 Expert

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    Hi all,
    No problem, simple enough to explain. The bacterial conversion of NH3 to NO2, and eventually NO3, is aerobic and can only occur in the presence of oxygen (you can see this from the formula, you've gone from three hydrogen atoms to three oxygen atoms and the definition of an acid is "a H+ ion donor", so this process will also reduce pH, more description here <http://www.skepticalaquarist.com/bioacidification>).

    Nitrate is the end product of this aerobic process, but you can potentially out-gas the nitrogen as N2 gas, this is an anaerobic (bacterial) process.

    It is theoretically possible for both aerobic and anaerobic processes to take place in the same filter. The sellers of Siporax etc will tell you that their media is optimal because as "mature biofilm" develops on it both processes will occur. Nitrification will happen in the outer skin of bacteria, and as they deplete the oxygen, deeper in the pores anaerobic denitrification happens. This is potentially true, but the "devil is in the detail", because we have to hit the "sweet point" where both processes can occur. If you keep all the filter media aerobic this balancing act becomes irrelevant, we won't out gas our NO3 as N2, but we don't need to, we have plants to mop the NO3 up.
    Perfect.

    cheers Darrel
     
  5. brumbird

    brumbird Member

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    Thanks so much! The other bit I didn't get was how the small increase in bio load would crash the filter....?
     
  6. dw1305

    dw1305 Expert

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    Hi all,
    It is back to the balance again, because for both aerobic and anerobic processes to occur in the filter you need to be at the sweet spot where dissolved oxygen is being depleted to a fairly low level. If flow drops, or you add more ammonia (your fish have grown, you've added another fish, you've added some medication, fed sweet potato, had a dead fish etc) the BOD will rise and ammonia will start to pass through the filter untreated, and build up in the tank water. Usually low dissolved oxygen levels start killing the livestock, but even the most tolerant fish will eventually fall victim to the rising ammonia levels which adds more ammonia and you enter a positive feedback loop of de-oxygenation, rising ammonia and death.

    The difference in an aerobic system is that in the same circumstances you need to add a large amount of ammonia to overwhelm the system. If you have plants even better, more ammonia stimulates plant growth, and greater plant growth takes up more ammonia.

    It is a much more stable and resilient system.

    cheers Darrel
     
    MirandaB likes this.
  7. brumbird

    brumbird Member

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    Darrel you are very kind to help me understand all this, thank you.
     

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