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TastySalmon
11-06-2013, 08:17 PM
I'm not sure if this is in the correct place or not. I think it qualifies as me wanting to know how. :D

My question really pertains to the coupling of intensive recirculating aquaculture and aquaponics. A fish culturist by trade, I have taken an interest in aquaponics recently.

One of the books I refer to commonly in my RAS designs, Recirculating Aquaculture, has a section on aquaponics. I am aware of fish and plant ratios, but I suspect the "rule of thumb" can be broken for ratios is adequate filtration, such as microscreen drum filters (or maybe even ozonation), are used.

The following quote from the book refers to UVI research on finding the appropriate ratios.

"When the rearing tank was stocked with tilapia at commercial densities (107 fish/m3), the daily feed ration to the system was so high that nutrients rapidly accumulated to levels that exceeded the recommended upper limits for hydroponic nutrient solutions (2,000 mg/L TDS)."

OK, so what happens when nutrient solutions exceed recommended levels? Has anyone on this forum had first-hand experience with intensive rearing densities and aquaponics that don't follow recommended ratios?

Again, I have to emphasize that I suspect traditional ratios can be ignored if adequate filtration is provided. Modern microscreen filters have the capability of filtering down to 40µ and have the full capability of resolving TDS issues, but, particles smaller than 40µ and dissolved nitrogen still persist.

UVI wasn't using any advanced filtration at the time of this particular research project, so their findings really only pertain specifically to their system's capabilities.

Thoughts?

dead_sled
11-08-2013, 08:58 AM
Hello and welcome.
I am not an expert in this field and I will not pretend to be. My understanding of this process is that balance needs to occur between the ammonia production, the nitrification process, and the nutrient uptake by the plants. The filtering helps to insure overall system health, efficiency, and reduces maintenance. The solid waste can also be utilized for its mineral content (mineralization).

If you haven't read Oliver's AP manual, you may want to check it out. There is plenty of great info there.
http://diyaquaponics.com/forum/viewforum.php?f=112

Hopefully some of the more seasoned AP pilots will chime in.

Aloha Don
11-08-2013, 10:45 PM
Like DeadSled, I am not the expert but my understanding of this...
If you have too many fish in the system without proper amount of plants to uptake the nutrients then the buildup could harm your fish.

Avarial
11-09-2013, 12:15 AM
Ok, just my two cents worth, and again, with out nothing but a lot of study under my belt

First off, TDS only shows a portion of what you need to know. What a fish is fed, is what will determin what it will break down into as a ratio of NPK(as well as micronutrients), as it was posted in another thread:

http://www.aps.uoguelph.ca/aquacentre/files/research-publications/OSAWG%20Report%202%20Fecal%20Waste%20Chemical%20Co mposition%20(Jun2007).pdf

Next thing to consider once you have determined the nutrient composition of said RAS system, is the plants. The short and simple answer here is each plant has a differant nutrient load requirement. Unfortunately, in all my searching, I have yet to find a database, that shows the nutrient load of any given plant in vegitative growth, and then its load in flowering.

Third thing to consider, is the RAS system in question has a volume of 264 gallons(1 cubic meter tank), and when you add another 264 gallons of grow bed water, you are effectively "diluting" that 2,000 to 1,000 mg/L.

Now if you were able to get your hands on a chemical analysis of each of the available fish feeds, and according to the above report, assume 75% of each of the elements will end up as fish waste, you could then determin what type of plants you would need to use up all those nutrients.

In writing this post, I am trying to give you a few things to think about, and the first is most people in this forum(possibly all) are not going to have a TDS meter to even know what their system is producing. Second, is the idea of doing a chemical analysis on their biofilter output, and then a second analysis on the water that is returning to the tank to know what their growbeds are removing from the water. I believe this information to be crucial to be able to run a high density fish system such as used in RAS, in conjunction with an aquaculture system.

TastySalmon
11-13-2013, 08:38 PM
Thanks for the thoughts. I will have to put some more effort into nutrient loadings.

In response to Aloha Don's advice: keep in mind that intensive aquaculture doesn't need plants. A properly functioning RAS tilapia farm can load their densities up to 100 kg/m². With proper RAS infrastructure, plants are not needed to maintain water quality.

Basically the root of my question stems from asking myself why more aquaculture companies don't implement aquaponics.