A Community and Forum For Aquaponic Gardeners

Large Koi tank

Hello everybody, my name is Mike and I’m new to Aquaponics and this forum. I’ve been watching videos on YouTube for about 2 years, have read one book with another coming, along with a DIY greenhouse book. Anyway, I wanted to just ask a few questions.

1. I think one of the main reasons I’m doing this is to build the giant plywood or lined cinder block Koi tank I always dreamed of, around 2000 gallons. My wife the gardener has left the technical part to me so I kind of fooled/spoofed her by saying that in order to supply the amount of grow beds (drain with bell siphons and Hydrocorn clay pellets) with the proper fish fertilizer that this large a tank would be needed when it is really about 250 to 400 gallons at most. Please keep in mind that I do not like ponds and looking down at the fish, as a former Fish nut (I use to breed discus fish) I like sitting and looking at the fish from the side. My wife loves farming vegetables and is always on me about going “overboard” on everything. So are the following statements true....

A. I will not need a sump tank because even if all the beds were filled at once the tank level would only drop slightly.

B. Even in a moderately stocked tank I may not have enough grow beds to “clean” the water so bio filters and swirl filters may be needed, I hope I’m wrong on this one.

C. Inside the greenhouse I plan to build (double plastic filled with air between layers hoop house) it will get cold in the winter (Pennsylvania) and a Koi pond propane heater will be needed. I know that running this could be costly but I don’t mind because I really want to build this giant tank and have a 1000 gallon propane tank that I use for the house. Also, heating all this water should also heat the greenhouse and allow me to grow tomatoes over the winter, I LOVE tomatoes.

D. If you see anything else wrong with this improperly sized system please let me know and thank you very much! If things go wrong and my Wife starts asking questions it would be all bad!

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Permalink Reply by George on December 18, 2015 at 5:17pm

A. Difficult to say since you didn't give the volume of the grow beds but probably true. The volume of water in the grow beds, if full, will be about 40% of the total volume of the beds. I have six beds, no sump, but I pump to only one bed at a time - this works for me because my tank is the low point in the system - I pump to the beds and drain to the tank. Is this what you intend to do? If not, you may need a sump.

B. Probably true, depending on volume of media beds, which are biofilters. A drum of bird netting or some other media with aeration can provide a lot of additional biofiltration. You just can't have too much filtering and aeration. I've come to believe that solids filtration is a good idea in any type of system.

C. True. Water will act as a heat sink.

D It seems to me that you're planning well. Good luck.

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Permalink Reply by Michael Pyle on December 18, 2015 at 5:37pm

Thank you very much.

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Permalink Reply by Pieter Swanevelder on December 19, 2015 at 1:15am

I'm currious to know the number of fish one will kept in a 2000 US gal/7000L system. If stocking is too low - the nutrients in the water will be very low with resultant stunted plant growth.

A reasonable pump should also be sized - depending on type of system

for a split system typical: FlowRate[Volume/Hour] = FlushCyclesPerHour x GB_WaterVolume/hour + 2 x FT_Volume/hour

with the FT loop going through filters (the residue could be added to the GB manually/or composting)

The formula is not set - depending on system set up - but one wants the FT to be cycled 1 - 2 times per hour.

Maybe considering splitting the large FT into smaller units - rather a few smaller systems with inter connectivity - than one larger system? Thus if something needs to be maintained you've got redundancy? It also allows for different fish/size to be kept seperate.