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PostPosted: Jan 10th, '19, 00:37 
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I was talking to an aquaculture expert who lives in my town. He reckons aquaponics is inherently inefficient, because the need to strike a balance between, and the inability to prioritize both plants and fish... Essentially RAS systems can be better than AP at producing fish, and hydroponics can be better than AP at producing plants.

While I can see how a balanced backyard hobby system for personal production can be rewarding and productive, I can't help feeling that this guy has a point when it comes to large scale production.

So why not split the loop? Run a RAS system, drain of the solids and part of the water on a regular basis, keeping nitrate levels within limits, and feed this into a separate hydroponic loop?

Some advantages to this would be that you could run the fish and the plants at different temps, optimizing production of both; you could amend the levels of certain nutrients for the plants without worrying about the fish; you could use pest control on the plants without worrying about the fish; you could drastically reduce flow in the hydro loop and save pumping costs...

Any thoughts?


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PostPosted: Jan 10th, '19, 10:41 
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I have been doing similar for a few years- drain off some fish poo rich water from the main AP circuit into a separate circuit with WBs, rather than hydroponics. It's currently got a stack of potatoes growing in it, pics in my big system thread.

In any case, I don't think that getting the absolute maximum efficiency from an AP system is the goal for backyarders, its being able to produce fish and veg in a reasonably simple system.

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PostPosted: Jan 10th, '19, 11:35 
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danny wrote:
So why not split the loop? Run a RAS system, drain of the solids and part of the water on a regular basis, keeping nitrate levels within limits, and feed this into a separate hydroponic loop?


Already being done by a few people for exactly the reasons you mentioned. I think it probably makes no sense for most backyard growers because it's tougher to maintain but would be a good idea for a commercial setup because it's more efficient (if you have a market for both fish and plants)

Dasboot has his system setup this way and has posts on the forum if you want to check out a system that's split. I don't have any posts about it but I got my AP system changed over to this last year so this coming year will be the first time I try it out for a full growing season.

danny wrote:
hydroponics can be better than AP at producing plants


If you prioritize plants I think your yields for AP and regular hydro would probably be similar plus you'd have fish. Prioritizing fish without increasing plants leads to excess nutrients that need disposal so then you start having to ask about waste treatment, environmental costs and are you really paying the true costs for production.

danny wrote:
you could drastically reduce flow in the hydro loop and save pumping costs...


I'm pretty sure you'd be increasing your pumping costs since you still have to pump the fish water and you'd need a second pump for the plant side (I use a third pump to get the solids to the mineralizer). You'd probably need an additional air pump for the mineralizer and much more aeration for the fish as well since your packing more in.


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PostPosted: Jan 11th, '19, 04:30 
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Seriously, this cant be healthy.
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Been doing it for years :lol:

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PostPosted: Jan 11th, '19, 08:51 
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You're just ahead of the curve Milne 8)

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Sometimes it's called a split system and sometimes it's called a dual loop.


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PostPosted: Jan 11th, '19, 20:55 
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Thanks for the comments guys, interesting stuff...

Considering a strategy like this seems to really broaden the possibilities for how a system can be run, especially in a rainy temperate climate like the UK where the main conditions that make AP so useful; lack of rain and lack of fertile soil, are irrelevant.

Using small water volumes for hydro loops, enabling warming with solar energy and season extension etc seems to be a massive benefit...

And I like the wicking beds; no need for circulation pumping, and utilising compost from solid plant waste

I wonder if there are any APers in the UK or similar climates who have explored the possibilities of a split loop system?..


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PostPosted: Jan 12th, '19, 02:03 
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I wouldn't be surprised but I don't know of any right off.

One thing nice about the wicking beds is they warm faster than the AP does in the Spring. The other part of this is that the AP goes further into Fall so the two make a good combination. My climate is a lot like yours, cool maritime climate. Many years I don't even need to worry about the system freezing in Winter but it rarely gets hot around here either.

It helps to start your plants outside the AP setup in the spring. Starts take forever in the cool AP system, if they come up at all or aren't consumed by damping off fungi.


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PostPosted: Jan 15th, '19, 17:40 
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I can see how waiting for the whole AP system to warm up would put severe limitations on early planting.

Aside from wicking beds, I suppose a split loop system could be used to overcome this; if the quantity of water circulating in the plant loop was kept small it could be heated passively or with an aquarium heater at relatively little cost.

That way wicking beds could be kept for root veg and plants that prefer soil, and hydroponics could be used for the rest that grow faster hydroponically.

In the autumn, in order to extend the growing season, a large body of water with accumulated thermal mass could be circulated. And perhaps using a solar powered pump could help minimize heat loss by only circulating in daytime and relative to sunshine etc.


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PostPosted: Jan 16th, '19, 05:32 
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Yeah, there are various ways to take advantage of the differences and you can also increase the AP temp by putting your system in a high tunnel or greenhouse. With all the thermal mass of an AP system used in a greenhouse you get less fluctuation in greenhouse temperature and improve the growing conditions for the plants. You also might be able to change what fish you choose to grow in your system. The downside of course is that trout probably won't work out in this environment because the water may become too warm.


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PostPosted: Jan 16th, '19, 05:47 
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Yes ideally I reckon you would want trout inside poly-tunnel/greenhouse during the winter and outside in summer, in my area at least.

Although you could have the tanks in an insulated indoor environment like a warehouse, with a split loop you would not need to subject the fish's environment to the temp fluctuations associated with being in a site exposed to sunlight.

Thermal mass could be provided in a poly-tunnel/greenhouse by other means.

Carp, perch and zander (similar to walleye I believe) are other options with a much larger temp tolerance range, the problem is they won't grow much when the water isn't warm.

I would love to raise burbot, but would need a place that could be kept very cool all year.


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