Aquaponic Gardening

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How We Build Our Solids Lifting Outlet (SLO) At Smoky Mountain Aquaponics

There are many ways to skin a cat or in this case get the poop out of your fish tank (FT). Here is how we make ours for our full size IBC (Intermediate Bulk Container) FTs. We wanted a true family size AP (Aquaponics) system so we went with five full size IBCs for our fish rather than cutting our grow beds (GB) from the tank top first. This also meant we did not have to make covers for the FTs as they already had covers. They just needed lids cut in:

So our system might be a bit different from yours but you can make those changes yourself. Forgive the abbreviation explanations but for newbies it really helps so I try to enlighten at least once for each.

First off there are 2 types of waste (actually 3 but we will address the main two while forgetting about "suspended solids" for this writing) in our AP FTs. The sinker solids that drop to the bottom AND the floaters that for numerous reasons tend to float at the top of the FT water. These floater are generally old fish food and any waste that is fermenting and trapping the CO2 along with oils. When one of our trout dies for whatever reason the first thing we notice is the oil slick on the water surface. Any of these can float and accumulate on the surface of the FT water and SHOULD NOT be allowed to build up for the sake of your fish. Then there are the sinkers that are heavier than water and sink to the bottom of the tank and of course should not be allowed to accumulate either. So what is the simplest way to address these two forms of waste and get them where they belong and that is down system and out of the fish's home? I think we came up with a pretty neat method.

Let's address the sinkers first as that is what most Aquapons are familiar with. Over time we came up with a very nifty and inexpensive way to pick up these heavier wastes and it came about inadvertently. I knew we had to run our drain line down to the bottom and I wanted to cover as wide an area of the bottom as possible while KISS (we live by KISS {keep it simple stupid} around here as there is always that human desire to make everything as complicated as possible and this tendency must be fought and fought hard). So after some experiments that all displayed some sort of "fail" down the road I simply ran our exit pipe (1 1/4" Thinwall PVC, cheap and more flow for your $) down to the bottom of the IBC and using a 90 across the bottom center of the tank. I put 1/4" slots about 1/4" apart along about 2' of the bottom of that bottom pipe on our trusty 12" Harbor Freight chop saw:

About that time I was perusing the aquarium supplies at our local Wallyworld (Walmart for the uninitiated) when I came upon the niftiest air stones. They came in 8", 12" and 16" long strips (all under $5) and could be plugged one into the other (daisy chained) for any length airstone. I immediately pictured these zip tied on top of my recently designed SLO PU pipe as air stones need to be tied down anyway so they don't move around or even float up. To be honest I hadn't even thought of the huge added benefit of doing that until I saw them in action. "I would rather be lucky than smart"

After a few days of operation I noticed how much cleaner the bottoms of the tanks were staying and how the waste was being drawn right to the PU pipe by the current created by the rising air curtain.  Let's face it sometimes we just get lucky. So now my trout were getting lots of air and the waste was getting out better than ever before. Of course you will still need to clean out the corners of a square tank like IBCs every now and then but the labor and duration between cleanings was cut by about 80-90%. Nice, because we would rather be fishing or just about anything but scooping poop. The more active the fish (trout are very active athletes) the cleaner the tank will stay as they keep the waste moving until it is drawn to the PU pipe. Here are some pics of our early PU pipes so you get another visual:

Slots too small in this old pic but you get the idea: The airstone is on top and slots on bottom. The pipe was too small as well (1")

These slots on the next pic are more like it: Put a cap on the end of course like first pic above. I use 1 1/4" THINWALL pipe now (nearly the same interior volume as 1 1/2" schedule 40). This all terminates in the 1 1/4" T that has a THREADED side entrance so you can use a threaded adapter and an "O" ring on the outside of the FT. Note the much wider (1/4") slots on the pic below:

I should also mention here that we use a 25' garden hose with a 30" x 3/4" pvc wand and a little ball valve just before the wand (a 45 helps to form a better angle on the hose) for a siphon for sucking any solids left in corners, etc.. Fill the hose with water, shut off the little ball valve until you have the wand in the FT  and open the valve and let it run downhill for a great tank bottom cleaner. Just shut off the little ball valve while switching between tanks so you don't have to fill it again. A fish tank vacuum if you will. Run the other end of the hose into a barrel if you want to collect this very rich water for your fruit trees or dirt garden. Very much like a swimming pool hand held bottom cleaner but no pump involved. If you are lucky enough to be able to run the hose down a hill you won't believe the power of this little "sucker"
Back to the SLO.
Now that we have the lower half of the SLO explained let's get to the floaters part of the SLO. In order to skim the floaters off the top we need a slot in the exit T right at the surface of your FT water level that will allow the smaller particles (like old fish food) and the oils to get out without dumping all the fresh fish food as well which is heavier and larger. Again very much like the skimmers on any swimming pool except more precise. I found it is not so easy to guess exactly where that slot should be SO I now cut about a 1/2" wide slot on the chop saw and later make an adjustable dam out of 2" pipe that slips over the T so I can absolutely nail the level and even play around with it later. We use a T for three reasons, that dam and so there is a "second chance" overflow just in case something gets plugged up AND so the SLO will not drain the FT dry if you loose power. It breaks the siphon. If the water level rises it simply goes over the top of the T and out. Here is a pic of cutting the slot in the T.  As I said I now make the slot bigger and adjust it later with a moveable dam:

That's about it. It meets the KISS principle and cuts way down on our (my:-) labor AND keeps the water clean for our fish. I don't know about you but I want the water in my FTs to be as clean of fish poop and all other wastes as possible. After all "we are what we eat and our fish are what they eat and we eat our fish" I know lots of people that say I am full of it but I try. Nuff said? Please feel free to ask questions and I will add more pics as time allows. Here is a graphic that might make it all a bit more clear: Here are a few more pics of my latest moveable dam. Cutting these pieces on the chop saw is a bit dangerous to say the least so unless you are very proficient at using tools this close to fingers please don't learn on a detail item like this. I have experienced nothing short of an explosion when a small part like this fetches up in the 12" saw but I have been doing stuff like this for over 45 years and I still have my fingers. Please be careful!

This pic shows the T and the dam.Another view.Looking thru the threaded tap of the T

This is an old pic but shows the T in place inside the fish tank.

The electrical "Threaded Adapter" (straight threads as opposed to plumbing thread which is tapered) mounted outside the FT

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Comment by Jeff S on September 20, 2014 at 11:19am

I was thinking about black poly but not sure how much heat I'm talking about. Would probably have to support it off the aluminum to avoid melting with an insulator of some sort.

Comment by Jim Fisk on September 20, 2014 at 8:39am

New to me too but Wiki says it is NOT for potable water and cPVC is the best. (less plasticizers).  So much to learn and sort out.

Well then the AL should be fine! Cool. What is the tubing material inside the AL to be?

Comment by Jeff S on September 20, 2014 at 7:51am

Thanks Jim. I'm just using it as a container for the tubing so it won't come in contact with the water. Not familiar with uPVC. Is that something to use for hotter water?

Comment by Jim Fisk on September 20, 2014 at 6:26am

Hi Jeff, IMHO I would stay clear of aluminum in your system. It corrodes like crazy and many MDs attribute such things as Alzheimer's disease to the heavy use these days in cooking. Cancer clinics won't allow it either. We threw our cookware out many years ago. I feel it would build up in the system. Now if your system water does not come in contact with it sure but if it does I would use SS as I do. Cast iron would be fine of course. Aluminum works ok in your engine block because it is starved of all O2 in the coolant while we add O2 to our systems at every op. Sorry, I too have plenty on hand but would not even consider using it in our AP. There are plenty of battles to be had without asking for trouble.

Now I have siphon customers asking me to make them siphons using uPVC speaking of battles. Need to find a good source. Any ideas? Wiki says to use cPVC for potable water which of course we use for HW here in the US but not in those sizes. I should ask Victoria at ASC as she has written books on the subject.

Comment by Jeff S on September 19, 2014 at 9:35pm

Jim, I need your opinion on material for my water heater box that I plan to run over the top of my wood heater exhaust stack. Is there any reason I shouldn't use rigid aluminum for the box since it's a very conductive material? I have lots laying around so it's cheap :)


Comment by Jim Fisk on September 10, 2014 at 12:38pm

Hi John, yes it is very important to filter out the fish

I use the drain to lower the FTs down to about 12" during harvest and I use a wok strainer on a piece of pvc, for a handle, to block the drain during that process. I haven't gotten around to figuring out a more permanent guard yet. Someday.

Comment by John Tracy on September 10, 2014 at 11:51am

What a great idea!  Thanks for sharing.  I'll be modifying my system next season, and this looks perfect!

I used the drain on the IBC for my outlet and never had a problem with the sinkers when I started the system with Koi and large goldfish last year.  I was surprised how clean the tank remained.  This year, I switched to tilapia fingerlings and had a BIG problem.  The fingerlings were swimming out the drain and got lodged in the plumbing.  I lost 12 good fish!  Live and learn.  I managed to screen off the drain to prevent more losses, but definitely need to make a change next go round.  Thanks, again for your informative post!

Comment by Jim Fisk on September 3, 2014 at 4:19am

Thank you Sylvia and Vlad. My favorite place to share AP. I'll try to get some more articles done soon. We have had a very busy Summer.

Comment by Sylvia Bernstein on September 1, 2014 at 2:27pm

Great post, Jim!  Thanks for your contributions in here.  It's guys like you that make this site rock. 

Comment by Vlad Jovanovic on August 29, 2014 at 4:41pm

Awesome tutorial Jim, thanks!

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