Backyard Aquaponics
A place to discuss aquaponics

Having burnt out one fairly new pump, I am trying to install auto siphons on my three growbeds and cannot get the right infow/outflow to make the siphons work.

My siphons will not remove the incoming water fast enough to keep the vacuum going. The water raises just above the siphon and then discharges.

I have tried varying the rate of inflow and the shape of the siphon loop (having tried looped tubing, 90º and 45º angled pvc). Nothing seems to work. If I plug the output hole with my thumb, I can fill the tank and it will empty correctly once. I have tried it with the discharge end of the pipe both in and out of the water in the fish tank.

I am beginning to believe that the issue may be the height of my growbed above my fish tank. The bottom of my growbed is only about two inches above the rim of the fish tank. Do I need to raise the height of the growbeds? (Please don't tell me I need to do this. They are filled with gravel and already planted.)

As I understand the auto siphon, the core concept is this: The growbed water level raises until it reaches the top of the siphon loop (does it have to be a loop? Can it be an inverted U?). When the water level reaches the top of the loop, a vacuum is formed in the tube and the water is pulled from the growbed until the intake pipe is partially out of the water and air is introduced into the tube. This breaks the vacuum and the process of filling the tube starts again. Can someone correct/expand on this to clarify what I should think about to correct my drainage problem?

If the vacuum is not strong enough the empty the tank, what do I do to increase the strength of the vacuum?

Thank you, as always, for your help.

RP the timing of your post is interesting. I just hooked up my first set of tanks this morning to get a cycle started on some fresh gravel and ran into similar problems. Here are the two problems that I had.

1. My pump was too small. When the tank would fill the auto siphon tube would start draining, much like an overflow, but the pump wasn't able to keep up so the tank never got ahead of the tube so a siphon could start.

2. The bottom of one of my drain tubes (bottom is about 10 inches below the siphon fitting in the GB had a small bend in it(from being rolled up in a coil) and the tubing couldn't purge itself at the end of the siphon.

With these two problems fixed, I'm draining ok.
Hope this helps, good luck.

- I don't think you need to raise the beds. The bottom of the bed does need to be above the water surface in the fish tank, but 2-3 inches should do it.

- Your description of the concept of an autosiphon is correct. I struggled a long time to get my looped autosiphons to work correctly. What finally worked for me was to exit the growbed horizontally, and make sure the final drop of the autosiphon is as vertical as possible. Your pump may be too small for the diameter autosiphon you have built. All of them will trickle as they start, and then kick in fully. I think mine trickle slowly and then faster for perhaps 15 seconds before kicking in. If they only trickle and don't fully start, then you need a bigger pump or a smaller diameter hose.

- Pictures would help with diagnosis of the problem.

- Actually, looking again at what Jazz has said, we're saying the same thing....

Place a restriction on the end of your siphon as a test. If it starts chugging properly then, then it is your pump and you have 2 options. Leave the restriction. Get a bigger pump. :-) hope that helps

Hi RpondPA,
Can you time how long it takes to fill the bed, and how long it takes to drain the bed when the siphon is working? What dimensions are involved? The diameters, volumes, and flow rate are crucial to it working reliably.

I am not sure what you're saying above, is it failing to start or failing to stop? Are you saying that the water is just draining out like a regular overflow? If it is not "kicking in" to a speedy out-rushing of water, then I would think your tube diameter may be too big for the pump flow.

A few inches of drop below the grow bed helps the water keep inertia going to maintain the siphon - if the tubing ended just below the siphon inlet I would expect it to not kick in properly. Think of the water column in the trailing end of the siphon like a freight train, being pulled downhill by gravity and pulling the rest of the water over the loop. If the front half of the "train" is too short it won't have enough inertia to keep the rest of the water column going.

RPP,
My 2c (3c AU) worth: Reduce your drop-to-tank section of pipe (or all of it...whatever). I changed from 1/2" PVC to 1/2" CPVC and the couple mm reduction in diameter made all the difference. You might try putting a 90 deg fitting on the bottom of the drop tube to make the water exit horizontally as this seems to help as well. With the larger pipe I never got it to work without a full U on the pipe exit to prevent air filling it back up: startup took three to five minutes after the bed filled: the smaller pipe takes 10 seconds from bubble to full flow.

I think one effect of low-water level diff might be to cause the siphon to fail (if it flows slower than fill rate or air can flow into the pipe). If it does work, it will slow as it nears bottom, probably giving you a somewhat longer dry time...this could be good.

Thanks all.

I know the pump is not too small. It's a 1000 gph pump pulled from my outdoor pond although not all of the flow ends up in the growbeds. If I do not divert some of the flow, the siphon tube cannot keep up and the bed will overflow. I have tried both a 3/4 inch pvc tube for the siphon and two different 1 inch flexible tubes.

I'll apply try your advice tomorrow and, if that doesn't work, post some pictures and the exact dimensions of the setup.

Janet, the tilapia you gave me seem to be doing well. The were timid at first but will now rise to take food almost immediately. Thank you so much for sharing your stock. I will order some in the spring and return the favor.

Since you are already diverting some of the flow the simplest solution is to adjust the diversion/bed flow balance until everything works.

Set outflow end of the siphon at water level in the tank to give max drop/max suction. Below water seems hard to start, far above it sacrifices suction.

An inverted U works fine.

Glad to hear the tilapia are happy. My breeders are getting along much better now that the male has a trimmed lip. The females are out and about rather than crushed into the corner trying to hide from him. That has to be better all around, but I still have no fry. So I may need the favor!

Janet,

What do you mean "a trimmed lip'?

Rand

Hi Rand,
I trimmed off the upper lip of my male tilapia so he cannot kill the females so easily.

1.) wash sharp kitchen shears well.
2.) remove male from fish tank and place in bucket of water with tranquilizer.
3.) wait 10 minutes.
4.) instruct husband to hold fish.
5.) pull upper lip (of male fish, not husband) out and trim it off with kitchen shears. (ick!) Trim from corner of mouth to opposite corner in the thin skin behind the lip.
6.) don't look and gross yourself out.
7.) return male fish to tank and apologize profusely
8.) realize the females are sooo much happier now that the male can't bite chunks out of them, and that they are hanging out with him better.
9.) think, hmmmm....maybe he'll get some, now.

You make that sound nasty. Do they bleed? I may have to do that with one of my males. He has staked out his pipe and is attacking all the other fish. They all stay huddled in the opposite corner.

What do you trank them with? Is is sold in normal fish store?

Hi Dan,
I tranked him with "Bag Buddies" by Jungle. It's really just clove oil and some salts. If it isn't available at the LFS, then you can get it mail order here: http://www.thatpetplace.com/pet/prod/214411/product.web

There was just a smudge of blood at the top of the lip where there's a tougher section of skin. Otherwise, no blood. And the male actually didn't seem to mind while we were doing it. I felt a bit cruel, but now that it's over, and I see the new tank dynamics, I feel much much better. All of the females were dark gray, and taking up the least space possible in the far corner of the tank previous to surgery, but now are scattered all around the tank and showing more relaxed colors. Funny how I can kill them and clean them, but not perform surgery, huh?

Dead is dead Janet, a job that needs to be done. Surgery is causing pain (perhaps) to an animal and expecting it to recover. If you killed your fish in a slow nasty painful manner, then sure I don't see why you have a problem with surgery, but I do assume you are fast and kind in dealing with your dinner

I off my fish as fast and humane as possible, of course.