Backyard Aquaponics
A place to discuss aquaponics

I agree that putting a hole out the side of a grow bed at your desired water level will probably not work well for you. Generally you will find that the hole is not big enough nor low enough to actually keep your grow bed from flooding too deep or overflowing.

If you must plumb through the bed on the side rather than out the bottom, you can still put an elbow and have a vertical stand pipe in the bed to set the water level if the elbow isn't high enough. This is what I've been doing on all my 100 gallon stock tank grow beds since I don't want to mess with trying to plumb through the bottom trying to get around all the bracing and the concrete blocks etc. Granted as I said before, my grow beds are really deep. I generally use 1 1/2" or 1 1/4" standpipe drains on my grow beds.

As to why I would keep the plant rafts away from the fish...
If you have a raft over your fish tank you loose the ease of being able to look into the tank at your fish to make sure there are no dead ones. You also loose the ease of just tossing food into the tank. Rafts on a take where you feed the fish tend to get fouled with the fish feed as well as fish poo. Dead fish can float up and be hidden in the plant roots and you may not notice until things get really bad.
The raft will cover the surface and require you to add much more air pump type aeration to keep dissolved oxygen levels good for both the fish and plants than you would otherwise need in the fish tank.
Some people have run into problems with fish jumping and managing to get up on top of the raft and dieing in the sun. Many types of fish will eat plant roots. With a raft on the surface of the fish tank you don't get to splash the incoming water into the tank as vigorously to get more aeration. Generally you want to avoid having fish poo collecting on your plant roots in a raft and some means to filtering the solids from the water before it gets to the plants seems to help.

Now I expect most of my poor performance in my raft bed is because it is hooked to a system with a hard water problem. The high pH tends to lock out the iron and the deficiency problem seems to show far worse in the plants without access to the media/worms/bacteria etc. Many people do run successful raft systems, generally the only fish allowed under the rafts would be mosquito fish who are expected to eat the mosquito larva and are not fed anything else (some people have also grown prawns under rafts but they are expected to eat detritus and not fed either.) They also usually have some form of filtration before the water gets from the primary fish to the plants.

Standpipe or Side overflow - definitely standpipe

If I had to plumb through the side at the desired water level to create an overflow, I would do it using a 2 or 3" pipe (depending on the ability to seal the hole you drill). The pipe would be rotatable and would go into the bed a short distance. The portion in the growbed would have the end capped and would have a slot along the length of the pipe for water to enter the pipe and overflow to the sump (this would take care of most volume issues with all but the smallest pipe). To change the water depth just rotate the pipe.

A standpipe is still way better, since you can easily and dramatically change the water levels for crops or to get rid of vermin. If you have an option go this route or do as TCL and I have with the stock tanks before you go straight out the side.



This is how my stock tanks are setup also (not quite as good as straight down but better than horizontal). Mine go through the side near the bottom of the growbed, not at the water level.

SLO issues
You can increase the flowrate through the SLO by splitting the outflow of the SLO. One portion would go to the growbeds and the other would have a ball valve and would go directly to the sump. This would effectively regulate the flow through the growbeds as well (so you wouldn't need the ball valve off the pump and would just have one outlet). Not ideal because of solids circulating back to the fish tank but they would eventually wind up in the growbeds. With a small sump and a large solids handling pump, accumulation in the sump should not be an issue.

It is possible that the sump could be pumped dry before water comes back from the overflow of the growbeds. You have to watch evaporation and the length of the pipes when you have a small sump in relation to the tank size. A carefully placed top up valve would help with this.

It really is amazing the amount of effort you all are willing to put out to help newbies like us. I really hope when I "grow up" in AP I can help out too. I love these conversations because based on "why" people would/wouldn't do different things I get to know more of the concepts behind everything... aeration, gravity's affect on water, etc.

Thanks again! I may just end up going the suggested 2GB on top of 2FT for my first system, but I'm tucking all this away for later.

May be put to vertical because the drain must go vertically at least 24" or so above the horizontal branch & then go to it with a entice above that level.

"because the drain must go vertically at least 24" or so above the horizontal branch"

does this mean you need 2ft height variation between 'steps' in the system? e.g. FT down 2ft to GBs down 2ft to ST?

i've seen various designs to get bell siphons working better, as well as recommendations about using fewer tight bends but nothing really about height requirements. i'd have thought while higher will produce more flow due to gravity, gravity is gravity and it all ends up down...

trying to avoid setting up all my FTs and GBs only to need to adjust all the heights later