Backyard Aquaponics
A place to discuss aquaponics

To download my plans you need to use the "click here" link I posted above (or now this one ->) to get http://BrainRight.com/Aquaponics/JaysTubes.zip. That zip file contains the JaysTubes.skp file that you can load into SketchUp after you download and install the program from http://SketchUp.google.com/

I took some pictures of the automatic shut-off system that I made. It uses a ground fault current interruptor (GFCI) to immediately shut off the water pump if it detects any water where it shouldn't be. The GFCI plus an extra outlet are contained in this box that mounts on the right side of the unit:



By itself, that would just shut off the power if it detects any ground fault in the things plugged into it. I added a connector at the top that exposes the hot side of the GFCI load through a 10K-ohm resistor to limit the maximum current to 12 milliamps (very important!), plus a ground connection. In the U.S. we have 120V power and GFCI devices will trip at around 5 milliamps, so this will trip the GFCI if the resistance between the leads drops below 14K-ohm or so (I = V / R). If you don't understand any of this, please don't try to build a device like this! You are responsible for your own safety.

A cable plugs into the connector and runs down to the bottom where it exposes bare leads into the plastic tray beneath the tank and also below a wooden block placed on the floor:



Any water across these leads will draw enough current to trip the GFCI and shut off the pump. I also run my light and heater through the GFCI just in case water shorts them out, but my air pump runs straight from the mains so a tripped GFCI won't starve my fishies for oxygen. So far I haven't had any leaks, but I sleep a lot better knowing that it won't pump water all over my hardwood floor!

very clever but like you said, I have extremely limited electrical knowledge and wouldn't build one of these myself

I've been thinking about the production rate of this system and, after I have some experience with it, it seems that I might be able to produce as much as 1 mature fish per week in my 29-gallon fish tank. I know that many people have large-scale systems where they're trying to produce a marketable crop all at once, but in my case I just want a meal for my wife and myself now and then so I'd rather harvest them one at a time so I don't have to freeze them.

I have read that under good conditions a tilapia can grow to table size (1 pound) in 6 months (26 weeks), and that a moderate stocking density is 1/2 pound per gallon. If we wish to produce one mature fish per week, that means stocking 26 fish with ages ranging from hatchling to mature, with an average weight of about 1/2 pound. That gives a stocking density of only 13 pounds in 29 gallons which seems reasonable, especially since I'm pumping in a lot of air and I have a lot of grow bed volume with good circulation.

The tricky part is maintaining a steady supply of hatchlings at a rate of about 1 per week. I'm fortunate that I can just buy them locally one at a time if I want. But I'd rather have the fish producing their own replacements rather than buy them, if I can do it without much stress on the system or on me. I'm thinking that I may just let the fish do what comes naturally, and periodically cull some fingerlings (whitebait omelets?) to maintain something close to the ideal population with a wide distribution of ages and no more than 1/2 pound per gallon. It would be totally impractical to do that in a big system but in a little tank like this it seems like it wouldn't be too difficult.

Any thoughts about this approach? Has anyone tried something similar?

Jay with Tilapia it would seem an entirely reasonable scenario....

Those things breed like rabbits without any external stimulii or particular environmental factors.

In a mixed-sex set-up, you won't be able to keep them from breeding! My concerns would be around the breeding activities in such a small tank with innocent bystanders in the way. The males can get a bit boisterous, and will stake out territory. Mine have started that already at about 3 months of age. Anything entering the territory (which would be about half of your tank) had better be ready to mate. Anything else will be driven off. The males have been known to injure and kill the females. Some references prescribe clipping the upper lip of the males to reduce injuries to the females. (That just makes me shudder.) I will be watching my breeders carefully, providing shelters for the gals, and be prepared to separate the breeders if needed. I'm getting ready to sort my breeders and spare females out of the tank this weekend. I have spotted a couple of the males already, and have ruled the largest one of them out as a breeder just because he has a bit too much attitude. There's a really good looking one that is nearly as large who is much more peaceful.

Cichlids in general (tilapia are a kind of cichlid) have some fascinating breeding behavior, but you need to give them room to do it, or some fish are going to get hurt. I have a 125gal AP grow-out set up, plus am adding a 50gal breeder tank (1 male, 3 females), and a 50gal fry tank. I plan on a fish meal for the family of four about once a week.

If you could buy 4 young male fish every month, that might be better.

you cant stop them from breeding for sure but the problem is the young fish eat the fry So you would have to provide a place for the fry 2 shelter.

Absolutely right, CG. I just figured the cannabalism was the least of his problem. He only wants a few survivors.

hey Janet do you mind going in to detail how your breeding tanks are ste up and how you chose your male/female fish

I have got to try this... it looks so simple...

Jay, where do you have it mounted? Are you getting enough light to the plants?

Mc

Hey CG. I'll talk about setting up my breeders on my own thread. Wouldn't want to clutter up this one.

MC, it sits in front of a southeast-facing window. That's the yellow rectangle in the drawing. Straight south would be better (in this hemisphere) but southeast is what I have. The tubes on the sides won't get as much sun due to the window frame but they should get 4 hours of full sun, and 6+ hours in the middle.

Have you thought about another small aquarium or large bucket for a breeding pair Jay, or if you had two buckets with a bubbler in them, you can have one as breeding tank, and one as small fry tank. The fry could be used as feed for your larger fish, while keeping the odd larger fry as replacements for the growout tank..

Mine have been breeding about once every 5 weeks, with the two 4 inch long females having about 50 babies at a time, thats a lot of fish..

Sorry to but in.... I moved a 2 inch tilapia today and low and behold it spat about 30 babies.... moved them to a glass tank to raise them. I am so excited... that and the new batch of convict babies....

Well done TimC/Female tilapia, hope they all grow strong and fat