Aquaponic Gardening

A Community and Forum For Aquaponic Gardeners

Hello all, 

This is my first post. Ive been super busy the last three years developing my system and have had great success. I am running a 30'x48' greenhouse, 'growing power' vertical bed style. I am enjoying my dual-root systems (soil pots) that sit in both deep media ibc totes and shallow media runs (see growing power model). I also grow AP classic style in just rock.I grew 1000+ pounds of watercress in shallow media bed, with river rock media last year! The dual root is highly advantages because I can give nutrients directly to the roots (mostly P and N) when i feel its needed without having to manipulate the water mass. I heat with a central wood boiler that I send hot water to my tanks' in-floor heating (insulated son the ground and then pex-al-pex separated by the plastic floor to my 'trench' tanks.) Ok i think thats enough info there...

My next big project is to grow ALGAE at a rate that i can use it to be the sole feed of my fish food, and see good growth rates of my fish (tilapia). I am currently NOT feeding my fish at all. They survive from the algae and inverts that i wash down into the tank from it growing in my shallow media beds (mostly filamentus). This is enough for the tilapia thrive and be healthy but not growth much. For this reason, i believe if can get enough algae into their gill rakes they will have enough food to have good growth rates. I am looking at having an IBC that has my culture (spirulina, so i can eat it too), in which i will give nutrients and co2, and then pump through thin-walled pvc tubing for sunlight, and return back to the IBC culture tank. The tubing will run the length of my greenhouse and attached on the structure. This is all done in a separate and independent loop than the AP system.

From there I will simply inoculate the tanks and allow the fish enough time to collect the algae in their gill rakes before i turn the pumps back on for the water to circulate the AP system, or better yet, i will have a filtration method to condense the algae so that the tilapia can feed on it at greater rate and efficiency. 50 micron screen is suitable for spirulina. 

If this works, I will have an endless source of the best fish food (and human superfood) on the planet!

Questions/comments for the public:

has anyone done this?

I know my obstacles to success are;

-growing enough algae to be effective

-making sure the algae doesn't overrun my system once in the water column (taking all the nutrient and oxygen),

-filtering the algae from the grow system at an effective rate... their are some sweet filters for bio-fuel industries, but a 50 micron screen works as well.

-Does anyone know of charts that can provide feed/growth rates with algae rich water for tilapia?

Well I hope this gets the conversation started. Growing Algae (spirulina) has infinite uses in horticulture soil science and human health potential. It can truly make our systems a bit more 'sustainable' if harnessed correctly. The power of the sun is all that is needed once its gets going...tho co2 and extra nutes may bump it up a bit!

Thanks for your time! happy gardening!

Justin at Sacred Valley Farm in Durango, CO

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That's a tough one Justin, your FCRs are typically based on dry weight of feed with high protein content.  Cultured algae is typically 96-97% water and low protein, so with a great FCR of 1:1.6 you'd want a feed with a minimum of 35% protein at at least 1.5% of total fish biomass daily.  So in this hypothetical situation for 100 lbs of fish, you'd need at least 1.5 lbs dry algae daily at 35% protein.  Protein around 10-12% is more likely, so you'd need around 4.5 lbs total on a daily basis for fish feed.  This means you'd have to harvest 4.5/(100%-96%)= 112.5 lbs of algae (wet weight) daily.  That's a lot of algae to replace fish feed.  If you don't care about fish growth you can use less, but you will start running into nutrient deficiencies in both your plants and fish at that point. . . it just gets very complicated.  Hope that's helpful!


Thanks for the response Nate, your awesome.

I am finding that spirulina is 60% protein (high), 24% carb, 8% fat and packed with Vitamin and Minerals. With a break down like that, would the feed reqs be reduced? Also do you see a discrepancy with the FCR being based on dry weight of highly processed feeds, this compared to a wet and living food source, one that tilapia are perfectly adapted (practically engineered) to eat? Still i think an obstacle or daily hazard would be harvesting or screening that much Algae, but with some screening techniques it could be simplified.
With 275 gallons of cultured algae (IBC not all the way full and 350 feet of clear thin wall PVC 2"), at 97% water , thats 8.25 gallons of concentrated, wet algae. I don't know how much that weighs, but a gallon of water weighs 8.34 pounds, that almost 69 pounds of concentrated wet algae. not too shabby...but thats for daily feed reqs...

I would also think that its worth its weight for fry and fingerling feed. Fry and Small fingerling are geared towards eating solely micro algaes and inverts in the wild.

I understand I will never achieve growth rates as found as standard in aquaculture, but definitely want to keep the conversation going about the potential of spirulina in a greenhouse. With the clear thin wall PVC getting more affordable, using the existing structure of a well built greenhouse seems like just another way for us to maximize space and yield. I Love consuming spirulina and I think its potential and power as a healthy food crop ( and possibly fuel crop) is fun to think about.

I going to start this project anyways so ill keep you all posted! Thanks again!


Sounds good.  Let me know how it goes!

This doesn't sound like a good idea tbh. The algae is consuming nutrients your plants could use.
Do you use a sump tank or filter system.? Put some water fleas in there, they will eat the algae.
And any that reach the fish tank. The fish will eat. Grow duck weed in a separate system I.E. tubs, bucket, ponds, ETC. Use that as fish food.

It is great that you are thinking in terms of replicating nature and using the free energy of the sun to create fish food. Algae and the planktonic crustaceans it feeds is an important part of the life cycle. But, I would say it is a building block not the solution.

I have experimented with algae and Tilapia and my results showed only a subsistence level of growth. To be fair, I am not sure if there is a threshold of how much Algae a Tilapia can take in or if I just did not have enough life growing in the tank. Based on Nate’s numbers above, I am assuming the latter. If I decide to give it another go I would culture entirely outside of the system to better record the feeding and for faster production. I was also considering building a Rotifer production system for giggles.

Algae is great but why monoculture? In the food chain there are many organisms that feed on algae. The fish feed on these organisms, so why not diversify their diet by creating several mini ecosystems with varying foods. It sounds like you have a bit of that going on already in your shallow media beds. I am a big fan of (Scuds) Amphipoda and the fish love them. These small organisms feed small fish and big fish eat small fish. I would not force a cannibalistic feed on my fish. I am however feeding Tilapia fry, runts, and fingerlings to Yellow Perch and Walleye. Once I have a decent population of these, they will return the favor and feed the Tilapia.

The sun makes the algae. The fry and young fish feed on the algae. Small fish are fed to big fish. Fish feed net cost zero. Well…to be fair, I cultivate insects, worms, and plants as well. They are used for supplemental feeding and to vary the diet. Energy costs are also a concern. I am beginning to monitor them with a sub meter. I am in the process of putting together a list of the plants and animals and the methods I employ to culture them. I plan to post it here when completed.

If you are raising Tilapia, you may want to consider live bearing aquarium fish like guppies, mollies, etc. They reproduce easily and will feed on the algae and the associated life it supports. The offspring make great fish food and I can’t help but speculate that it would be healthier for the fish than a pure algae diet. 

I would suggest you keep the algae you grow for human consumption separated from your aquaponics system. Spirulina can be infected by toxic algae so you should test it regularly to make sure it is safe. A smaller batch is easier to monitor and test than an entire system. You can also more easily regulate light, temperature, and ph to optimize growth in a smaller space.

I am very interested in your project and would love to hear about all your successes. Thank you for sharing.

Did you ever do this?

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