Public Greenhouse aquaponics system proposal.

[James Keller]

So here is my sketchup for a system I've designed.  Background: There is a new vertical greenhouse that will be built in downtown Jackson, WY.  It will be on a 4500 sq ft plot, and go up 3 stories.  (verticalharvest.org)  The public will be allowed access to the first floor, and the top 2 floors are going to be used to grow hydroponic vegetables.  

My idea is to get an aquaponic system in the greenhouse for public education and to build interest in aquaponics.  

I would propose that they set aside roughly a 10' by 10' space for this project.  My design has a few unique factors, first is the L shaped fish tank in the foreground, which will house native trout, and be set up to mimic the trout's natural habitat.  Also, I chose to separate the grow beds into 3 different types of bed (flood and drain on the left, constant flood in the middle and a float bed on the right).  

The initial issue I foresee is how to keep this water cold enough for the fish - are there water chillers out there that could cool the roughly 300 gallon fish tank?  Also, would the vegetable plants dislike 45 or colder water temps?  I know these trout need highly oxegenated water, but I haven't built any kind of aeration into this system yet.  

I have no idea if they will even look at this idea, but I think it will be worth at least nailing down a design and then attempting to present it to the people who are building this greenhouse.  I designed this fairly quickly today, so any comments on this design would be welcome!  

[TCLynx]

I can see that James.  And in most of the constant flood beds I have run.  I kept the ability to pop the stand pipe out and let them drain down on occasion too.

[Bob Campbell]

Are you using a constant flood in a media filled bed?  

How deep do you keep the water and how deep is the media?

How long has this worked for you?   

I can see why you would want the ability to flush it once in a while

James Keller said:

My small system started out as a flood and drain, and then one day i decided to remove the bell siphon and let it run constant flood.  Everything did great (except the strawberries, but I think that was a bad batch anyway).  So I would have no problem running a constant flood with this external bell siphon in my large system, simply by removing the cap on the siphon or drilling a hole in the top.  However, I do like to keep the ability to "flush" the media grow bed every once in a while to make sure there aren't any "dead spots" in the grow bed.  This may not really be an issue, but it makes me happy to know that I can do it every one or two weeks.  

I would also argue that with certain plants that I directly seed into the media, that I would get a more constant germination rate with constant flood since I know right where that water level is at all times.  Any thoughts?

[James Keller]

Hey Bob - I have a small 1 by 2 foot media bed, 12 inches deep.  I set the water level about 2.5 inches below the rim of the container.  Hydroton media filled to the top.  I had it running well with a bell siphon for a few months, and then one day just took the bell siphon out so the water constantly drains out of the existing drain pipe.  It's worked well for me for at least 3 months.  Every couple weeks, I just drop the bell siphon back onto the standpipe and it drains the grow bed, then i remove it again.  I was able to grow tons of lettuce, basil and a few cukes.  

Because I had planted some veggies from seedlings from a nursery, I did run into some aphid issues that never really went away, and my fish were overwhelming my bio filter (which i accidentally plumbed into the system with no ability to remove it and clean it).  These are the main reasons I decided to seriously upgrade and build a whole new system in another room in my basement.  I moved the fish over to the new 110 gallon tank yesterday!

[TCLynx]

Yes, I am using constant flood in media beds.

How deep depends on the situation and what I am growing.

I've done some constant flood 100 gallon Rubbermaid stock tank beds.  Those are 24 inches deep and I tend to fill them all the way up with media and I will normally set the sand pipes at least 2 inches below the top of the gravel.  I keep the stand pipes removable so I can adjust the height if needed.

I've also done water plants in shallow tubs where I only put 3-4 inches of gravel in the bottom and have the water about 3 inches above the gravel.  This worked well for water chestnuts but had issues with algae in the summer when there was no water cress to shade the water so I added the plastic drink tops to help shade the water and reduce algae.  I currently have a DWC bed that I never got rafts for where I have plant pots with gravel in the bottom for anchoring pond plants and there is duckweed growing on the surface to keep the algae at bay and enough shade from the pond plants to keep the duckweed thriving in the heat so far. 

The main thing with growing regular veggies in a constant flood bed is you need to keep the top of the gravel dry.  If the water is flooding up too near the surface of the gravel and the top of the media is staying moist, it will grow algae and can cause more problems with things like fungus gnats and many plants have more trouble with their crowns and stems being constantly wet and causing rot so if doing constant flood for normal veggies, make sure the bed is properly topped up with media or lower the flood height to keep the top dry.

[Bob Campbell]

Thanks TC,  Sounds like you have experimented with just about every situation.

Do you need a fairly good flow through the media to avoid what James called dead spots?

TCLynx said:

Yes, I am using constant flood in media beds.

...

The main thing with growing regular veggies in a constant flood bed is you need to keep the top of the gravel dry.  If the water is flooding up too near the surface of the gravel and the top of the media is staying moist, it will grow algae and can cause more problems with things like fungus gnats and many plants have more trouble with their crowns and stems being constantly wet and causing rot so if doing constant flood for normal veggies, make sure the bed is properly topped up with media or lower the flood height to keep the top dry.

[TCLynx]

yea I would recommend a fairly good flow rate.  Over on BYAP Creative1 who has been doing constant flood for ages recommended at least like 9 liters per minute I think.  So if you stuck with the flow ranges recommended for raft beds you will probably be ok (between 2-5 gpm through the beds)

I've been addicted for aquaponics for years, and I have tried plenty of things.  There are plenty of things I'll say, here look at this, DON'T do it that way.

[Averan]

I'm referring to the same test by Murray Hallam that you are thinking of. That and my own system which I've disabled the siphon and left running constant flood for many months now with no apparent effect other than that I don't lose nearly as much water to evaporation!

TCLynx said:

I don't know what real world tests have proven siphons less productive than constant flood.  Can you share links for such examples?

I do know that some real world tests have shown constant flood to be not much less productive than the two different flood and drain methods.  The three methods side by side in a very small scale test only showed minor variations in performance between the three methods.  With constant flood perhaps providing quicker system cycle up time while the plant mostly did best in the timed flood and drain while some plants still did really well in constant flood and the general outcome of the test was that all three methods WORK.

[TCLynx]

Murray didn't do the test I'm talking about.