Aquaponic Gardening

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I have a 55 gallon aquarium connected to a 30x14 inch grow bed.   In the aquarium is 4 x 8" blue channel catfish, 4 x 4" goldfish, and at any time anywhere between 1 to 75 rosy reds (to distract the catfish from the goldfish).  Ive gotten to the point where pulling the catfish out and weighing them is impractical since my brothers girlfriend told me that the aquarium was an "eyesore" and insisted I decorate it.... So, there is driftwood and artificial plants used to hide the plumbing.  I estimate their weight around .34 lbs a piece so 1.36... lets just say 1.5 lbs of fish in total in the aquarium.  Anyway, I recently went away on business and upon my return noticed that my plants are not growing anymore.  Pull out the API kit and...

Ammonia, 0
Nitrites, 0
Nitrates, 0

I use an Arduino micro controller with pH probe, pH raise solution (hydrated lime/water), and pH lower solution (muriatic acid/water) with dosing pumps to regulate pH between 6.8 and 7.2.. this works well so I know there is no nutrient lockout.  

Obviously, there is no nitrogen in the system and that is the issue.  

My question is twofold: 
How many more fish should I add and would it be acceptable to go and catch fish from a private pond or lake and put them in there in the mix?  I would obviously quarantine the new fish anyway I go but would love to have something semi nice in there.  

Any suggestions?

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I'm familiar with Blue Catfish and Channel Catfish and both grow to large size but I don't know what a Blue Channel is.  Your stocking is limited by your filtering, which you probably know, so you can either use the rules of thumb on this site to get a general idea of how heavy you can stock or you can stock until it becomes a problem and then either do water changes, get rid of fish, or add filtering.  In my view, you're better off stocking lightly so as to have a safety margin but if you want lots of fish, then add lots of filtering.

Consider this:  It may not actually matter how few fish  you have or even if you have any, if your main concern is feeding plants.  Composting worms in your media can do the work of breaking down uneaten fish food so definitely get worms if you don't already have them.  If you read the posts by Converse, you can learn a lot about it.  For this to work, your pumping system must be capable of getting the solids to the media.  

Your need for nitrates may vary from time to time, depending upon your gardening, so it's good to be able to increase or decrease feeding, as needed.

In my system, I have few fish, compared to my filtering capacity and use an airlift pump to pump solids.  I generally overfeed and worms do much of the work of breaking down solids.

It sounds like you went out of town and the fish weren't being fed - not usually a problem.

good luck

The catfish will be dinner at the point they get to be "marketable" weights.
I MAY have gone a bit overboard on this but this is what I have done.   I have added 2 bluegill to the system, 1 was 105g the other is 92g (now). Yes, I weigh my fish when possible.  I also added a significant amount of blood meal to the grow bed to organically raise ammonia.  I like the idea of adding more fish, feeding and then checking my levels daily to see where the "sweet spot" is in my system.  Ideally I want to eventually sell these start up systems and advise my clients but I need to determine optimum conditions and parameters first.
 Readings today were:

Ammonia: .50ppm
Nitrite: .50 ppm
Nitrate: 5.0 ppm

Oh, and at the moment there are about 90 rosy reds left from adding 100 today to the mix.   Those bluegill are pretty impressive hunters.  The fish goes in, and scales come out by the gills.  Pretty cool.

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