Aquaponics on a fish farm

[Vincent Seah]

Hi,

I'm currently testing a floating platform which I built on an existing fish farm as an experiment. However, the results have not been good, am hoping to get some advice here.

Here are the details:
Size of platform: 2 meter sq (less than 1% of the entire coverage)
Plants used: Mint, basil, dill, red cabbage and various ornamental flowers
pH level: varies between 6-8 depending on time of day
Ammonia level: minimal
Nitrate level: minimal
Types of fish: Ain't sure about this but the owner did assure us that there are a variety of fishes in it
Temperature: 28-32 degrees Celsius
Growing media: soil
Climate: Tropical throughout the year

Symptoms:
Yellowish leaves
Slow growth
Stunted growth

Have been testing this for 3 months but can't seem to figure out the problem.

Please note that the fish pond is in an open area and there are subjected to every environmental conditions.

[Chi Ma]

You may not have enough fish density to provide nutrients. The biomass already in the pond probably uses up all the fish waste the fish generate.

[TCLynx]

Perhaps some pictures would help.

[Vincent Seah]

Just like to ask, is there a rule of thumb on the fish density?

Chi Ma said:

You may not have enough fish density to provide nutrients. The biomass already in the pond probably uses up all the fish waste the fish generate.

[Vincent Seah]

Here are some pictures

TCLynx said:

Perhaps some pictures would help.

[Vincent Seah]

More pictures

[Debra Colvin]

By the pictures of the roots there, I think you don't have enough of an oxygen flow for the plants.
That problem alone hinders their ability to absorb nutrients. I've no experience with dwc myself, but I do suggest getting some sort of a water circulation going. Somehow.

Maybe a solar powered water pump?

Your set up is a nice one, btw.

[RupertofOZ]

Lack of nutrients.. to some extent...

Lack of oxygen.. to a major extent... (especially with temps 28-32 degrees)

Root rot... inevitable...

[TCLynx]

Get an air pump and put some air stones down below your rafts.  DWC (Deep Water Culture) or Raft culture always needs supplemental aeration.

Fish density, Well rule of thumb is really designed for the recirculating type of aquaponics system.  It gets much trickier when you are talking about a natural pond without the recirculating aspect.  In pond culture you are limited in different ways.

Get your hands on a freshwater master test kit and run some water tests and that will better help us to make recommendations.

by the way you can post pictures directly in discussions using the image icon which happens to be at the top of the post box next to the Link button like this

[Francois Lemmer]

Hi Vincent
You mention growing media as soil......

That is the  1st thing I will get rid of.....change

Yust me thinking

[Chris Smith]

I tried for a year to get aquaponics to work with my koi pond with the same results you are having. Once I built a proper aquaponics system I was successful immediately. I believe that aquaponics does not work well with ponds because of the sunlight hitting the water and the anaerobic areas. Sunlight hitting the water will cause algae to bloom during the day consuming nutrients. Ultraviolet light will kill the beneficial bacteria. During the night the algae dies and begins to rot which consumes oxygen. Ponds of that size will have large anaerobic areas which will consume oxygen day and night. The more oxygen to the roots the better. Your pic shown sever root rot probably due to lack of oxygen.

 It may be possible to try a floating wicking system. Have pots of media suspended above the water on rafts and have a wick going from the media down into the water. The wick will draw water to media and keep the roots wet as well as oxygenated.

[Vincent Seah]

Actually, I am noticing that too, and am wondering why. The same plants I plant it in my backyard with a filter and aeration seems to be flourishing.

Thanks for all your suggestions and I will look into that.

Chris, there is a rule of thumb to make this work actually, you might want to experiment on that. In order to control the algae growth, and the condition of the water, one must cover 75% of the surface area exposed. After which, the algae growth and death will be controlled.

[Chris Smith]

I gave up on experimenting on my pond years ago. I actually stumbled onto aquaponics when researching bio-filters for my pond. I now experiment with aquaponic systems.