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PostPosted: Dec 17th, '18, 23:19 
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So I've been working through various costing exercises for a hypothetical commercial system which i would like to turn onto a reality a few years down the line.

The idea is trout in round tanks, RFFs, static up-flow/mbbr filters and DWC troughs. All in a poly tunnel, possibly passive solar design, and/or small wood-burner which would double up as a smoker for the fish... in the hotter summer months the sides would be raised in attempt to mitigate as much as possible against rising water temps.

Anyhow, I have been reading up on feeding rate ratios (for DWC) and have come across a remarkable lack of consensus; with recommended ratios ranging from 13-100g feed/ m2 growing area.

I was wondering what people make of these figures? Also, given that most of these recommendations are based on warm-water tilapia production, how they may differ in the case of cool water trout production in a temperate climate (southern England). The plan would be to supplement lighting and keep water warm enough for fairly decent growth in the winter.

Any comments appreciated!


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PostPosted: Dec 18th, '18, 11:40 
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There are a lot of variables. Tilapia feed is probably around 32 percent protein while trout feed is usually 40 percent protein and the protein in either is probably about 16% nitrogen (which is what the plants use). Whether you mineralize and re-introduce any nutrients from the solids you take out in a Radial Flow Filter or other filter. The feed conversion efficiency and so on...

I would definitely try to mineralize any solids you take out and then re-introduce them. That should reduce the amount of feed you need per square meter of DWC. In some of the studies, at least part of the solids were removed from the system by cleaning the filtration.

I'm not sure how warm your system will get in the summer but rainbow trout die at a water temperature of around 75 F/24 C.


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PostPosted: Dec 18th, '18, 14:08 
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Find a start point and experiment

Water test equipment

Brix measurement might be your best option measure plant health

https://permaculturenews.org/2011/11/24 ... -need-one/

Some more Info here this crowd are selling stuff

https://blog.nutri-tech.com.au/the-beauty-of-brix/

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viewtopic.php?f=18&t=12070


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PostPosted: Dec 18th, '18, 20:29 
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Cheers guys, I guess it's of course inevitable that there is a lack of consensus with so many variables at play.

The brix measurement with refractometer sounds like a good method and tool. And of course, experimental system mark 1 will be key to gaining confidence for scaling up, for the time being I'm figure crunching while I still can't set up a model system. The question here was regarding possible distribution between fish tanks and grow space in order to make rough revenue forecasts etc... all very theoretical so far of course, but important to be familiar with the numbers I guess.

My goal would be to sell directly to consumers on a local basis (my town-folk are affluent and ethically driven consumers... you know the type!), and not to be totally skewed towards plant production because I believe there would be a market for the fish in my area.

About solids and mineralization... Given that southern England is very seasonal, I was thinking about mineralizing solids and using the juice as a base solution for a separate hydroponic system for nutrient hungry fruiting plants. This way I could make nutrient adjustments without worrying about fish health, I could warm the water more effectively and to higher temps to extend the growing season, and I could run it at a lower flow rate, saving energy compared to having all in one loop. I could run this through summer only, partially shading the leafy greens in the DWC, and in winter give DWC all the full sun available and store up the mineralized sludge juice for the following summer. Of course I could re-introduce a percentage of the juice in case of deficiencies appearing on leafy greens.

About heat... It would be touch and go in the hottest and longest of the heatwaves, and an emergency back up plan would need to be in place. However, as a reference there is a non-heated outdoor swimming pool in my town that never goes past the 20-22 degrees C mark (I believe), this pool is fully exposed to sun, but also wind, so evaporation cooling may keep it down a little... at any rate, 24 C is higher than our high monthly average for mid summer, so it should be possible I think.


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