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PostPosted: Oct 15th, '20, 15:31 
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Hi,
Newbie here hoping for some guidance. Any help much appreciated.

I am hoping to put a pond in the garden (Latitude 45 western WA USA), for trout. Proposed pond will be 50x35x10ft. I plan to use a commercial liner and I will aerate with an air pump.

I am planning to use grow beds with total volume of about 40cu ft for biofilter and to use nitrates. I will also have some plants in the pond for landscaping. I hope to put the grow beds in a greenhouse to maintain temperatures above freezing in winter and with some hope that I can keep the temperature acceptable for trout all year.
So assuming the above: 40cuft is ~300 gallons of biofilter/grow bed, which the rule of thumb might suggest I can maintain about 60lbs of fish..?

Does this seem right?

How do I work out the desired pump performance?
Presumably I need to maintain a certain flow rate through the biofilter/grow bed, perhaps this is based upon residency time in the filter?

Many thanks
Beardy


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PostPosted: Oct 17th, '20, 08:49 
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Gidday Beardy, welcome to the forum.
Here’s some info for you that should be of help.
viewtopic.php?f=12&t=6646&hilit=Rules+of+thumb
Hopefully you will document your build here for us to follow.

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PostPosted: Oct 17th, '20, 09:51 
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Hi Skeggley,

Thanks for the Welcome, but I've read you referenced thread at that doesn't seem to make sense...

If I used an IBC of 275 gal. then I could pump that in an hour.
If I have the same number of fish in a different volume of water why should the flow rate be determined by the amount of fluid? Sure it's determined by the amount of fish food I am throwing in?

Pumping to turn over a 275 gal. IBC in one hour is one thing.
Pumping 131,000 gals of pond in an hour seems excessive...


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PostPosted: Oct 17th, '20, 11:53 
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Hi mate, remember they are only rules of thumb, not hard and fast rules. Generally people go for max fish for their biofilter and this is where these rules are more applicable.
My understanding, and I may be wrong I frequently am, its the fish that cause the ammonia transfer not so much the feed and you are right 5 fish in an IBC doesn’t require the same filtration as 25 fish, of the same size.
I don’t turn the water over every hour but I do have the required biofiltration.
If you want scientific specs then that’s over my head and can’t help, I like a comfort level and don’t push limits so much.
If you had 2000 trout in your pond would turning over the volume every hour seem sensible?
I know of large dams where the biofilter is the dam walls, the surface of the water is the oxygen transfer and they have no problems. Except birds of course. ;)
I’m sure there would be calculations and perhaps some of the brainiacs of the forum can be of more help.

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PostPosted: Oct 17th, '20, 15:09 
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Well I appreciate the interest and value the ability to stand on the shoulders of giants - all insight from someone with experience is useful to me.

Is there a good guide to the time taken for the water to flow through the grow bed - maybe one can infer something from the speed at which the flood and drain people cycle would be a starting point? Should be able to convert that to flow rate if we get a sense of the water volume in the grow bed?

That way I could put as many grow beds as I can reasonably fit and then size the pump accordingly...?


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PostPosted: Oct 18th, '20, 07:56 
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There used to be a really good crew here on the forum all loaded with knowledge however most have moved on in time and unfortunately it seems you’re stuck with us part time hobbyists.
:dance:

Ok, digging deep into my AP memory I googled a few names looking for some reading for you Beardy.

Here’s something from Wilson Lennard that may be of assistance.
https://www.aquaponic.com.au/Fish%20to% ... ratios.pdf

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