Notes from Windward: #69


Duckponics '09

Patrick improves our mid-level aquaponics system

     When I first came to Windward, Duckponics was a project I was immediately interested in. Coming with a background in irrigation and a long time love of pond works and hobby aquariums, I was excited for this was a chance to explore this area at a level I had only dreamed of. Much was in place already, but much was still left to do, and still more was yet unknown. Before I jumped into Duckponics too deep though, I had an opportunity to work with a smaller system already in place here, Barrelponics.

     Barrelponics is a study in theory and mechanics. Many projects here start out this way, small. It's a great way to test an idea, a mock up if you will, before making any larger commitments. With anything you do, especially in the presence of unknowns, there will be mistakes. Mistakes, loss, fails, whatever you want to call them, are not necessarily bad if you choose to look at them in the right light. We learn so much from our mistakes and the process of correcting them. This is why starting small works so well for us, small projects = small mistakes = small loss. Once the problems are worked out at the small level we are ready to move on to the next level. So, after getting my hands dirty with barrelponics making some minor changes and additions I had the understanding necessary to more confidently move over to duckponics.

     As I said above, so much was already there. The duck pond, the flood tank, the two large vegetable grow beds, and the smaller duck weed tanks as well as all the tubing, electrical, and drainage. This spring, during his apprenticeship, Jon played an important role in getting duckponics up and running for the first time. So, when I started working on it in early summer, it functioned well, but I wanted to advance the system to achieve its true operational vision. Initially, I focused on getting the holding tank to trigger a flood properly, a better dispersion of water to the grow beds was wanted, working out an appropriate timing with the automatic pump system both in frequency and duration was needed, and inflow and outflow still had to be worked out.

     After all this was done effectively (which was much easier after my experiences with barrelponics), there was a whole new gambit of unforeseen challenges to address. Such as, with this abundance of vegetation right there in the open, it invited many local critters to our hopeful feast: the ever present ground squirrels wanted the cucumbers; the yellow jackets wanted the water; and even our own ducks couldn't wait for us to harvest the duckweed for them and were raiding the tanks prematurely. So, it was obvious that protective covers were a must. We made these out of cattle panels and chicken wire and they have proven pretty effective so far.

Patrick adds chicken wire to the cattle panel covers

     Another challenge we faced was an increase in our duck population this summer. As so many of our systems and projects are integrated with each other, when we decided to increase our duck flock for another study, it had an immediate/unforeseen effect on the water quality of the duck pond. We didn't see the maturing of adolescent ducks as a problem until the increase of all their feathers clogged up our pump and caused it to burn out. So, a box filter was made out of an old milk crate and some mesh screen off a satellite we deconstructed for our solar boiler project, and it's working great so far.

     As far as the yellow jackets are concerned, they are an ongoing challenge, not just here but all over the Pacific Northwest this year. We've tried many things, from trapping them, using natural borax, avoiding them, even cursing at them. Nothing truly works against something that just doesn't stop coming. Our best solution has been to dedicate a shop vacuum to the sole purpose of "round-up." In the middle of the day when they are really active you can just sit there with the vacuum hose and catch them by the hundreds. The great thing about this is you can clear most of them out of an area you need to be working in, and because no poisons have been used they can be fed to our Guinea hens as a supplemental feed which saves us money.

      Anyway, so much has been learned at duckponics, and STILL there is so much to address, but that is what's great about this approach and how it will better prepare us for a potentially larger project.

October 19:

Working out the flood mechanism

      Ultimately, the purpose of duckponics is a study of bio-chemistry, just as the smaller barrelponics system is a study of theory and mechanics, both being necessary steps as we move towards a full operational and production scale integrated aquaponics system.

      Before we could really start to understand what the larger duckponics system had to offer, we had to get the water flowing properly. So, at the holding tank there were several things to figure out. Water in: drill hole, install fitting, attach hose from pump, so far so good. Water out: drill hole, install fitting, route to various grow tanks, easy! Flood trigger, hmmmmm?

      There were several ways we found to get the trigger to happen but many of them required too much constant attention and were unreliable. How could we get this thing to run on its own while keeping it as simple as possible? What we were working with was a two inch outlet at the bottom of the flood tank with PVC pipe routed to the various grow beds. An old float flap from a toilet tank was used as the stopper to this opening. If you've ever looked at one these things they are basically a bathtub drain stopper with an open ended inverted cone underneath to act as an air bubble for buoyancy to keep it up once in the open position. They work great in small toilet tanks, but in the 250 gallon cattle trough we use as the flood reservoir, the amount of water flowing through a two inch hole has enough suction to overpower the relatively small air bubble and close it immediately. It's hard to explain this part but in going back and forth between opening and closing the flood trap is where it all comes together. Being that we were using toilet technology we were trying to make a mechanism for a smaller system work on a larger one.

      So we set it up with a chain attached to a larger float at the top of the water level that when raised by the increasing water volume would open the lower flapper hatch. It worked great, except for that vast increase in escaping pressure that I mentioned before. As soon as the flood hatch was opened the water level of the tank would lower and so would the tension on the chain holding the flap open and it would slam shut well before the trough could drain completely.

      This brought us to the next challenge: how to make the air bubble in the flap larger in order to hold it open against all that suction? Luckily the solution presented itself rather quickly. We had a three inch hollow aluminum ball with a hole in the bottom hanging around from a previous project. We took a bolt of appropriate size, wrapped the threads in water sealing Teflon tape, and plugged the hole. With this bolt hanging out of the ball, now we had a place to tie it off in sequence to the toilet flap. About three inches above the flap this ball floats in the rising water. The ball doesn't have enough buoyancy to open the door on its own, but once the door is open by the upper float, it keeps the door open until the water level drops below that of the ball and the door shuts, readying itself for the next cycle.

      Once we resolved the flood trigger mechanism, it occurred to us, isn't the surface of this flood tank just a bunch of open water going to waste, what could we use it for? Barrelponics had the solution. The top level of barrelponics is an adaptation of a form of hydroponics where a floating raft is used to suspend root masses of plants in nutrient enriched water. So back to the shop we went and found some left over scraps of two inch Styrofoam from a previous project and constructed two oversized floating rafts which we cut holes in for root masses and connected with a piece of old cattle panel and then tied this off to the trigger mechanism for the flood tank. So now we still have our top float to open the flood door but now it is a raft of more vegetables instead of a float from a toilet. Ok, cool, the water is flowing, what's next?

the combination grow raft and float

October 21:

A few words on water flow challenges

     Another challenge that presented itself even after the basic water flow mechanisms were in place was the effect of the rate of water flow. We have a submersible pump that pulls water from our duck pond up to our flood tank. The pump delivers water to the tank through a one-inch pipe that connects to a 3/4 inch inlet fitting.

the inlet to the flood tank

     This works fine, however, there is a point when the upper float applies enough pressure to the hatch chain to begin opening the rubber flapper door that releases the water to the various vegetable grow tanks. That door is a two inch hole that is diverted to two different pipelines that have ball valve that allows us to control the rate that water flows from the holding tank into the grow tank. If those ball valves are fully open, enough water escapes through the lower port so that the water level in the flood tank never reaches a level where the upper float completely opens the hatch door for the duration of the flood.

ball valve flow adjuster

     So, after much tinkering, we were able to close the ball valves just enough to hold back the escaping water long enough for the pump to trigger the full open flood while still having the ball valves open enough to deliver enough pressure to power the water delivery tubes for the grow beds. If it isn't one thing it's another!

October 22:

Water distribution

     So now that the water is flowing and everything seems to be going fine, we need to look at how the plants receive that water. First of all, it is important to know that in any hydroponic system, it is the water that delivers the nutrients the plants need, not the soil. In most hydroponic systems a lot of money is invested in purchasing additives and nutrients for the water, and even more is spent on purchasing special neutral growing mediums such as Hydroton or Vermiculite. That is why we use water from the duck pond, the ducks fertilize the water for free, and in the process the plants filter the water and return cleaner water for the ducks' enjoyment.


     Also, we use pea gravel as our growth medium as this is more cost effective, more natural, and supports the nitrifying bacteria needed for the necessary biological process of converting ammonia to nitrite and then to nitrate. Pea gravel also makes a great low grade filter.

     While we were getting some of the other parts in place and working properly, we were delivering the water to the grow beds as a direct flood to the edge of the bed, you will probably see this in some of the early photos. But as I've said before, the long term vision was for something more sophisticated than this and through experimenting with the setup, we more fully realized the benefits of a "prettier" delivery. Basically, with the pea gravel acting as some what of a filter, if all the water is dumped on one side of the grow tank the nutrients may be unevenly distributed throughout the tank resulting in uneven plant growth.

watering system in action

      So, back to the plan. If you have a circular grow bed, one of, if not the most efficient, method of dividing space is to quarter it off. Instead of dumping the water from a tube at the edge we connected four tubes with a central intersection. We capped the end of the three dead end tubes and cut holes in the side of the tank to hold these tube ends up.

      Now came the tricky part. From previous observation, we noticed that with sufficient pressure these holes in these tubes acted like spray nozzles, damaging any small plants that were in their line of delivery. The solution we came up with was to drill the holes on either side of the top of the pipes so the water shoots up at an angle and then adjusted the pressure to make sure none of the water flow was directed outside the tank. By using an upward arc in the water we use gravity to pull the water back down to the plants at the speed of rain which every plant is essentially used to.

October 23:

Protecting our pump

     It was stated earlier that at a certain point this summer there was a significant increase to our duck flock and this had some unforeseen effects on the pump for duckponics. It was all those baby feathers that eventually clogged up the turbine in the pump and caused it to burn out. We don't want to get rid of the ducks, so what do we do about the feathers?

     Well, we cleaned out the duck pond as best as time would allow since other projects (such as watering the main garden and keeping the thriving cucumbers and mint alive in the grow beds of duckponics) depend on the functioning of the duck pond. However, no matter how often we may endeavor to go through a full scale pond flush, the feathers as well as other debris still come back to haunt us, quickly.

     We don't know yet if it is the total solution, but we think it is part of it. The box filter. Basically we took an old plastic milk crate and cut mesh screen pieces from a satellite dish to fit on all six sides. We wired them on, cut a custom hole to receive the pump, and attached the two together before resubmerging the new pump.

      I don't know if you've seen the screen mesh that old satellite dishes are covered with but the holes are pretty small. Still large enough for plenty of water to move through but just small enough to keep the feathers from getting to the pump. It still requires some checking in on but we would rather clean off the box filter every couple of weeks than replace the pump just as often.

      Also on the drawing board is a possible cyclone settling tank that would allow the silt to settle out before being delivered to the flood tank.

Notes From Windward - Index - Vol. 69