Sunday, May 30, 2010

Building the greenhouse

Hello everyone,

I'm relatively new to aquaponics, less than 1 year of experience. I started off by experimenting with an NFT technique and then moved to a system with a fish tank of 2500l. Photos of the NFT method can be seen here:
And for the last experiment with 4 grow beds:
our latest if of course on this blog:

In the flood and drain system we had 4 grow beds and about 100 carp fingerlings to start off with. However, half of them jumped out during the first two days for some reason. After that things were OK for quite a while. We grew some nice veggies but nothing like what I read about in this forum. I think the problem has to do with nutrient levels and feeding habits. We did not really feed the fish enough, and the food was probably of poor quality. Mostly rice and wheat bran mix. But since the system had no particle filtration the water quality became quite poor. Monitored levels of Ammonia, Nitrite and they were nearly 0 ppm. Nitrate less than 5 ppm. pH around 7.5 to 8.

The new system we are starting to build can be seen in the attached photo. I'll describe the components:

Grow beds
The grow beds are built from 'kadappa' which is a stone slab that's stuck together with metal paste. It's used as a drain here in India. Size is 2 x 2 x 1 foot. We plan to use 54 grow beds of this size.
The tank is calculated to be 12000liters. We have an existing pool that we are walling off to the right size for the experiment. A 1 HP pump will be circulating water through a 1" pipe through the grow beds. 3 rows of pipes will have 54 valves (one over each grow bed) to adjust the flow. From our first experiments the flood and drain system with the siphon stopped working after time. We though to make it simple this time, just a couple of smaller holes at the bottom of the pipe for slow draining and set the top height so the bed never overflows (2" below the top of the bed, or 1" below the gravel)
The beds drain into a 4" pipe that will return water to the fish tank.

The fish tank
The size of the fish tank is about 5 m x 2.4 x about 60 or 70 cms (depending on how we adjust it to keep fish tank: grow bed ratio). We are planning to buy an aeration pump with flow rate of 40l/minute and about 10 air stones to help aerate the tank. A question about the fish tank: Is more surface area and lower depth better than more depth and a smaller area? What would be the ideal minimum depth? We still have plenty of space to play with, the existing tank is 12 m x 4 m, and we can use as much of it as we need.

Sump tank-like thing
Since the tank is below ground level and we wanted to minimize the cost of the system, the best idea we had so far was to wall off about 2x3 feet of the tank, and join it with the tank through some 1 or 2" pvc pipes at the bottom. Somewhere half way up we'd install some sort of mesh to keep large particles from leaving the tank, and then above that the pump would suck out the water for circulation. The logic behind this is that a slow suction at the lower end of this tank would pull in debris and larger particles, and it would settle in this tank allowing for easier removal.

We though to put in 1000 carp, but maybe 500 is a more safe bet.

That's a problem here because you cannot get commercial fish food at that quantity and at an affordable rate. From research on the net, we saw that aquaculture in eastern asia feeds them mainly rice bran with groundnut cake. But it's very all very small particles that float on top of the water and probably that's part of the reason our test system is so dirty. One idea was to put the food in a mosquito net to hold it together and have them peck it out. Suggestions are welcome.

That pretty much sums up the system so far. We are currently clearing the area and masons are coming to build our walls next week.

Building up the grow bed stands

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