Aquaponics

Anyone who has made the mistake of asking me about aquaponics realizes quickly that once I get started, it’s hard for me to stop.  That’s why I haven’t written anything about it earlier.  But so many people have asked for the details of my trip to Florida (and I’m assuming they weren’t just being polite) so I’m going to tell you all about it!

On Sunday, September 6 I flew into Tampa and arrived at MorningStar Fishermen (MSF) where I would spend just over three weeks learning about aquaponics both in the classroom and through hands-on experience.  Monday morning I joined several other men in MSF’s classroom where we learned from Mark all about the theory and mechanics of aquaponics.  It took us the whole week to go through hundreds of PowerPoint slides, and we learned all about stocking ratio, pH, designing aquaponics systems, breeding Tilapia, macronutrients and micronutrients, adding nutrients for the plants without harming the fish, nutritional requirements of Tilapia, troubleshooting problems, water tests…

It was very helpful information, but we all looked forward to occasional breaks to feed the fish, test the water or vacuum fish poop out of the tanks.  Looking at slides is fine, but you really have to grab a few fish before you learn how to tell if it’s male or female!

After an intense week in the classroom, most of the students left.  Jon and I were left to manage MSF’s eight systems without them.  Let me tell you, I learned far more in the time that followed as we fixed clogged pumps and messed up siphons and experimented with our own ideas.  Together we built a model raft system (which is what MSF uses) and a model flood and drain system.  A raft system has plants growing on a foam raft with the roots in a tank of water (no fish with the plants – they’ll eat the roots!).  It uses far more water than a flood and drain system, which can be a good thing since it gives you more wiggle room with water quality and temperature, but it also uses far more space.  It also requires vacuuming fish poop out regularly.  A flood and drain system grows plants in gravel or another grow-medium in a bed that is flooded with water from the fish tank and then it all drains back into the tank.  The gravel traps the fish poop, which in time mineralizes and provides more nutrients to the plants.

I want to use a flood and drain system, so I need to move the fish poop.  That eliminates a water pump, which will only pump water – no poop.  This is where airlifts come in.  An airlift uses air pressure to pump water from the fish tank to the plant grow bed.  You make one by running a PVC pipe from the bottom of the tank up to whatever height you need to pump the water to.  You drill a hole in the bottom of the pipe just big enought to push in tubing for an aquarium air pump.  The rising air bubbles create suction and lift the water.  The problems: you need more than twice water depth for the lift you require, you need lots of air volume and pressure to get enough air down that far (you need a blower), and even so the suction is not very strong.  Bottom line: it moves water and fish poop, but not very efficiently.

After getting back to Pennsylvania I spent some time online and learned about the geyser pump.  A geyser pump is a modified airlift, where the PVC pipe runs through an outer bell (capped at the top) and an inner bell (capped at the bottom) and the inner pipe has a large hole drilled in the bottom.  The air tubing goes in the top of the outer bell.  When you place the pump in the water, the inner pipe fills with water.  As air is pumped into the outer bell, it begins to force the water up and out the top of the inner pipe.  When enough air accumulates in the bell, a large bubble bursts through the hole in the bottom of the pipe, which rapidly pushes the water in the pipe out the top, which also creates a lot of suction at the bottom of the pipe.  I made one of these pumps and moved water at about 3 gpm, lifting it 19″ from 16″ of water, and all with a tiny little airpump rated for a 60 gallon aquarium.  Translation: I can power my whole system with one little airpump ($40) instead of a blower ($400), and my emergency power backup can be one car battery instead of a bank of batteries!

Okay, back to Florida.  Now I have the move water and fish poop problem solved… what mechanism do I use to time the flooding and draining of the plant grow bed?  Jon and I learned all about autosiphons when we built our flood and drain system.  Without going into all the details, you drill a hole in the bottom of your grow bed and put a 1″ pipe in with the top of it at the level that you want your water to reach at maximum flood stage.  You drill lots of holes in a 2″ pipe and place that over the first pipe.  It lets water through without letting the gravel get through.  Then you cover the whole thing with a 3″ pipe, capped at the top, with a couple of large holes in the side near the bottom, and with a section of aquarium tubing that goes in the side of the pipe near the top and goes down to the bottom, strapped to the 3″ pipe so it won’t move.  As the water is pumped into the grow bed, the level increases until it hits the top of the 1″ pipe.  As soon as it goes over the top of that pipe, suction is created that pulls water from the holes in the bottom of the outer pipe.  The water will forcefully drain out in one shot until the level goes down to the bottom of the aquarium tubing on the outside of the 3″ pipe.  When the water level gets that far, air gets in the tubing and breaks the suction.  Now the water will begin to fill the grow bed again.  This is how you can flood and drain the plant grow bed on a repeating cycle without using any electricity (other than what you use to power the water pump).

So now I’ve designed and redesigned the initial system that we will build when we get back.  We’ll see what it looks like when it gets built!

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