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  1. #1

    filter to pond ratio ? Contact time ?

    Hey guys!
    whats the correct pond to filtration ratio that is needed. ? is it true that the Biological filter must 1/3 of the total pond volume ? Also what is contact time 😌 is it the time needed for the nitrifying bugs to convert the ammonia to Nitrite to Nitrate ? Im sorry newbie here😃



  2. #2
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    There isn’t really a correct ratio. It depends on many different factors.
    If you wanted to create a veggie filter or anoxic filter as your main bio filtration then a large filter will be necessary. However at the other end of the spectrum a shower with a very porous media such as BHM can be relatively small compared to the pond volume and have a small footprint. Moving bed filters with dancing plastic fall somewhere between the two, as do chambers of Japanese matting etc.
    Its also going to depend on how heavily you stock the pond with fish.

    Dwell time is something that there’s a lot of disagreement on. Some people strongly believe the water must spend long enough passing through the filters for the bacteria there to remove all the ammonia and nitrite before it comes out of the other end. Others believe this really makes no difference as if any ammonia or nitrite passed through it would simply enter again, and the biofilm will denitrify the water at exactly the same rate in either case.

    Personally I think it’s more about pond turnover rate and flow- you need a fast enough flow to draw waste towards your bottom drains and avoid dead spots in the pond.

    Traditionally a whole pond volume turnover rate of between half an hour and 2 hours is recommended. If you fit variable rate pumps and overspec these so they mostly don’t need to run flat out, you then have the ability to tinker with flow rates to find what works for you. You do need to make sure you have enough bottom drains and a mechanical filter that can allow the necessary flow rate though.

    If you base your calculations on being able to achieve a 30 minute pond turnover, and then find it can’t quite deal with that flow rate once it’s all working in the real world, you will still be ok for under 2 hours usually. If you plan for 2 hourly but find it doesn’t live up to that you could be having to redesign it all in the long run. I believe in building in a certain level of redundancy that you think you won’t need at the outset.

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  4. #3
    I agree. When anyone tries to tell me that there must be a minimum contact time of x number of minutes for biological media, I remind them that there are two biofilters that have good reputations; the Nexus range and Bakki Showers, then ask them consider the contact time for any particular drop of water as it passes through a Nexus or tumbles over the media in a shower. Then I ask, since both contact times can be measured in seconds, how does that fit into the theory of a minimum contact time which is measured in minutes.

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  6. #4
    Quote Originally Posted by Manky Sanke View Post
    I agree. When anyone tries to tell me that there must be a minimum contact time of x number of minutes for biological media, I remind them that there are two biofilters that have good reputations; the Nexus range and Bakki Showers, then ask them consider the contact time for any particular drop of water as it passes through a Nexus or tumbles over the media in a shower. Then I ask, since both contact times can be measured in seconds, how does that fit into the theory of a minimum contact time which is measured in minutes.
    Yeah, thats whats on my mind too sir since that filters are so small and yet its working perfectly for big ponds. But a lot of people here really believe in contact time of atleast 15minutes they said ..

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