Aquaponic Gardening

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Hi all,

Have an IBC tote system with 50 goldfish and clay pellets in the media bed.  All has been well for the last month.  Plants look good and are growing, goldfish have been healthy.  This week however a couple of things have

happened.  The tank looks like it has a thin covering of green so the water looks dark but the water is clear and several fish have died.  I have one large aeration stone going 24/7.  The water temp is around 70 degrees. 

My ph is 6.9

Ammonia is between .25 and .50

Nitrites are 0

Nitrates are between 40 and 80

I have consistently used a product call Organic Digester.

I have red wrigglers in the media bed.

Is the "algae" on the walls of the fish tank harmful?

Any thoughts or suggestions would be appreciated.



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At first glance I notice your tank is not painted. Sunlight coming through the sides will encourage algae growth. Is that your only bed?, if so it's too small. A thousand liter tank, should have a thousand liters of grow bed. Put a screen around the tank, add more grow bed, and make sure the water does not peek above the gravel.


Thanks for your response and suggestions.  Certainly a learning experience.  I enclosed the tank and covered the exposed area of the top so that's done.  Will now start working on adding more grow bed, would adding a raft for lettuce count or would that be in addition to? 

The more vegetation you add, the less nutrients available for algae growth. Doesn't matter if raft or media. Although media gives bigger area for bacteria to colonize. Cut down on fish food for a while, to slow down nitrate production till it's sorted.

Is this a new system? It looks like you haven't cycled yet.

Hi Mike, On top of what Paul has said I am concerned with your statement "I have consistently used a product call Organic Digester."??

Do Not add anything that you are not sure is FISH SAFE, EVER.  3 yrs in constant operation and I have never added anything of that ilk and you don't need it. Let nature take it's course. The algae on the sides is healthy. Ever looked at a stream? Plenty of algae on rocks, etc. in there as well if it is healthy. Now if your water gets to look like bright green pea soup you will need to add a simple mechanical filter to remove the majority thru simple filtration. I have a section on that here:


The system has been running for a few months, first with fishless cycling, then fish, then plants and worms in the last month.  My readings a few minutes ago were PH - 6.9, Ammonia - .25, Nitrites - 0, Nitrates - looks closer to 40 than 80. 


I will take your advice on the product, thanks for the information.  The water is crystal clear, the plants look great and are growing, the fish are active.  Thank you for clarity on the algae, much appreciated. 

Great Mike, I think you are fine. You can always expect a few fish deaths during start up and especially when adding fingerlings. Adult fish are far stronger and will put up with even poor ph. But always ck the ph before adding babies. I learned that the hard way. Remember that a young system tends to go alky and a mature system tends to go acid after say 6 - 12 mos. I have always used ashes from the GH wood stove to bring it back down. Once your system stabilizes it doesn't take nearly as much watching. I only ck ph before adding new fingerlings these days. You get used to the right smells and color of the water and even that changes from season to season and you get used to that as well. Have fun.

Thanks Jim, I am having fun despite the stress of a new system and lack of experience!!  The next forseeable challenge is going to be the summer heat! 

Get some tilapia and they will eat the algae and it almost impossible to kill them. I finally had some fish die this year. I did not add the heaters this year. Cold killed them.

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