Aquaponics

We converted our fist tank to a nursery to raise the tilapia which are now breeding.

We've had great results with Basil, Mint, Green Onions, Cherry Tomatoes, Watercress, and Chard with June and July being our best producing months. Depending on how you look at it, our system is producing between $300-$500 a month in greens. If you subtract $70 a month in expenses (Fish Food, Electricity, Mineral Supplements, Planting Media, and seeds) it still seems like it could be worthwhile to do on a larger scale. If we scale everything 5 times larger, we're starting to move into some significant savings.

There's many different ways to look at our savings. For example, we've been using 8 pounds a month of mint. Our kitchen doesn't buy organic mint because it's so expensive so it's not really saving them any money. It does have value of course, hence the Value and Savings columns in the spreadsheet. Our power consumption also has various interpretations. Given Kalani has 50KW of solar panels, do we really consider the cost of the electricity we're using, or do we consider it free.

Is it time to expand yet? I think the economics would say yes, but we'd like to solve a few of the problems I'll talk about below before moving forward.

We're also getting more people involved. Many people here at Kalani are curious about how the aquaponics system works. In addition to the property tour that Barcus gives on Monday at 1pm, I've started what I call "Aquaponic Tuesdays". About once a month, on a Tuesday, I invite all kalani volunteers and guests to come learn about aquaponics by lending a hand with some of the day to day activities. Here, Shola, Aubin, and Hillary help out loading net pots and planting seeds. I hope to open this up to the community at large in the near future. Please contact me if you want to come help out before then.

Planting Cycles

We've been learning about planting cycles as well. Seems like our Basil and Tomato plants reached the end of their productive life in August. Because I didn't realize that was coming, we'll go through a 1 or 2 month lull until the new ones I've planted start producing. Going forward, I'll re-plant 20%-25% of our tomato and basil crop every month to make sure we always have producing plants. Similarly, I learned with Onions that I need to plant them more often. I planted a whole months worth at once, but towards the end of the month of harvesting the onions were looking a little too old to be useful. From now on, I'll plant 50-100 every week or two to keep the flow going.

Root and Pest Problems

While we're having success with the crops above, we're still having pest problems with kale and all the members of the cabbage family. Our lettuce is still bitter sometimes. And we're having root issues with all the rest of our plants.

What's damaging the roots? I often see lots of snails and shrimp on the roots of our plants and have also notices that the mosquito fish have been breeding like crazy. Could any of these critters be damaging the roots? It's not talapia in the troughs as many of you have suggested. I have completely drained the troughs and no talapia were present.

I did a little experiment to see what could be damaging the roots of the plants. I wrapped 4 different rafts with screen and put root damaging suspects in 3 of the isolated rafts. The first was filled with aquatic snails, the second with mosquito fish (in our case platys), the third with Gammrus shrimp, and the fourth with nothing as a control.

Control ------ Fish ------S nails

The plants with the snails showed the least root development. Now, most of the gammrus shrimp died in my containment screen so that part of the experiment isn't valid. But I think I can say pretty conclusively that the snails ARE a problem.

Why are we having a problem with so many snails when other aquaponic systems in the area have snails, but no problems? I think I've discovered the answer and look forward to testing it in the coming months. Every other aquaponic system I've seen has a solids settling filter before the fish water enters the growing troughs. I do not. I believe that the solids entering the tank are breeding snails (and gammrus shrimp for that matter) like crazy. The population has gotten so out of balanced that they start eating everything they can including tender new root growth. This is further evidenced by looking at where the snails are in the troughs. There is a continuous gradient of snails and snail egg sacks from one end of the trough to the other with 4-5 times as many at the end of the tank where the solids enter.

I had not wanted to remove any nutrients by removing the solid wastes. It appears that it may be necessary though. So next on my list is to make a solids settling filter and net tank to capture smaller particles. We've already planted a row of papayas near our fish tank, which are heavy feeders, to take advantage of the solids when we start taking them out.

Battery Backup

One morning I was feeding the tilapia fry when I hear an alarmed "...that's not good..." from my boss Barcus as he opened the lid to the main tank. The entire surface of the tank was covered with dead tilapia ranging from 1-3 pounds. All told about 70 lbs or half our fish had died :( The circuit breaker had tripped over the weekend and it was caught a little too late for some of the fish. I quickly moved from searching for someone to blame to realizing that this is a great lesson for us. This incident made it painfully clear the necessity for a system to automatically switch over to battery backup in case of an emergency. The fact we learned this lesson with our small experimental system could save us many hundreds of pounds of fish from dying in the system we intend to build.

I designed an automatic switch that turns on an inverter and switches over power to the air and water pumps in the case of a power outage. An alarm is played as well to notify any in the area that there is an issue with the power that needs to be solved.

All this was done with a 3 pole double throw relay, an 400W inverter from the auto store, a float charger to make sure our batteries are always charged, a pickup truck backup beeper, and some miscellaneous wires and connectors. All told, the unit was about $250 including a 120Ah deep cycle marine battery which should give us about 10 hours of backup time. More batteries can be added in parallel for longer run time.

Alternative Fish Food

Whew ...a lot has been going on around here. The last endeavor I'm going to tell you about in this blog is our attempt to raise Black Soldier Fly larva to use as fish food. I attended a free seminar on raising BSF and we decided to give it a try here at kalani given our large supply of food scraps available from our kitchen. I doubt it will save us a lot of money, but as far as the principles of sustainability, to turn a waste product back into food, the idea is golden. The owner of the BioPod company who gave the lecture was kind enough to point us to a DIY web site to make our own BioPod. I made two to give it a try, we'll let you know how it goes. Details to make your own are here : http://blacksoldierflyblog.com/