Backyard Aquaponics
A place to discuss aquaponics

I decided to try DWC (Deep Water Culture) as a new home for my goldfish that have been moved out of the big tank to make room for edible fish. To me, the biggest benefit (for smaller sized systems) of DWC is the constant water level. I am going to be using a 200L drum with the top cut off as the tank (giving me about 140L of usable volume), so keeping the water level fairly constant is very handy. Also the UGF takes up space at the bottom of the tank, so the fish have even less volume to swim in (probably around 100L).

After reading some of the other DWC threads by AA (main one here) I thought I would give it a go, although I am going to add about 60L of gravel grow beds setup as flood and drain with an auto-syphon. This will allow some leafy greens to be grown and to keep the bacteria levels more constant as I will have the UGF (Under-Gravel Filter) and the gravel in the grow beds.

Currently I have made the tank and the UGF, the fish are in and we are waiting for it to cycle. Once that happens I will get the grow beds plumbed up and we should be going.

The UGF is made from the top of a 200L drum (not the top of the tank) with LOTS of holes drilled into it. I was going to buy a UGF but the drum I am using for the tank has a lip around the bottom, about 10cm above the floor (you can see this in the top section of the drum in photo). I thought this looked perfect for the "mesh" to put the gravel on and I had a drum top lying around which is quite thick, so out with the drill and about 1 1/2 hours later, UGF mesh made. I forgot to take photo's and it is now covered with about 10cm of gravel, so it is going to stay there.

Nova

At the moment, the tank is setup (UGF and pump) and the fish are in. The pump is just returning water to the tank as I haven't got any beds/tubs setup. This will be fine while the UGF cycles as the gravel there will house the bacteria which will then spread to the beds when they are plumbed in. I made an accidental venturi for the tank with the valve I am using to slow the pump flow a little. Some of the fittings must leak a little as the water returning to the tank is full of little bubbles. Just goes to show you have unexpected wins every now and then.

Nova

very nice

Nice set up! was just about to ask for spec drawings of the venturi and then read your post fish look happy

The water that will eventually travel to the grow beds is drawn from below the false floor in the fish tank, is this correct??

That is right. The water is sucked out from under the gravel by the pump (you can see the pipe going into the gravel in the pic) and it will then go to the DWC tubs and the small F&D tubs. I will be using 20L drums for the DWC containers.

The venturi happened by accident, all it is made from is 2 15mm-1/2" PVC adapters with the tap in the middle and 2 elbows. One of those joins leaks, except that instead of water coming out it has formed a venturi and is sucking air into the water. Bonus!!!

Nova

How large are the holes in the false floor, to you envisage any problems with solids blocking the water flow through to the pump?

Probably a stupid question, just trying to get my mind around this

The drill was something between a 1/4" and 3/8", about the diameter of a pencil. There are about 300 - 400 holes (guessing), they are roughly 2cm apart in a diagonal pattern. I doubt they will block up.

EDIT - I am kind of annoyed that I forgot to take a photo now.

Nova

Thanks Nova, good idea

Well the tub is starting to cycle slowly. I have been monitoring the ammonia and nitrite levels since the fish went into their new home 8 days ago. I put some gunk from my indoor cannister filter into the tank last wednesday, I just poured it into the water, the gunk went straight into the gravel, no cloudy water at all.

I did a few water changes (10-15%) early on, before monitoring, and then a larger one last friday as the ammonia level was at 2ppm. Changing about 40% of the water took it back to nearly 1, and it has stayed roughly there since. Haven't seen any nitrites yet.

I was expecting to see the nitrites rise and the ammonia levels fall, but I have seen no nitrites at all, and the ammonia levels seem to have stayed around 1ppm. I was curious today and I checked the nitrate levels and found I had about 7ppm nitrate. I guess the gunk has brought some bacteria into the system, as I have nitrates without measurable nitrites. Just need to wait for the little fellas to build up enough to keep the ammonia at 0 as well.

Coming along nicely, except that I will need to set up the beds and DWC tubs earlier than I thought.

Nova

I would have liked to have seen the UGF. Sounds like a nice setup...

I have just tested the water and it has cycled. Ammonia is at 0, as is nitrite levels. Nitrate is sitting around 15ppm. I added some shell grit last week as an experiment, the pH is now reading 6.8 instead of the usual 7. I assume this is due to the nitrification rather than anything else, the water is still crystal clear, no algae at any stage.

Just need to add the grow beds and the DWC tubs now. Although I may try some foam rafts until I can get everything else sorted. Does anyone know if goldfish will eat the plant roots?

Nova

Oh, great looking fish, Nova ! Those goldies did have access to some vegetable matter every so often, they might just develope a liking for plant roots.

They are hungry little fish. They have just gotten used to the new home and are starting to get more adventurous at feeding times. I have fed them duckweed too, maybe I will try a couple of plants and see how they go.

Nova

Well the nitrate levels are over 20ppm so I had better hurry up and get some plants in there. The pH is still less than 7 though, maybe I need more shellgrit.

I ordered some hydro pots the other day and they arrived late last week, just need a frame and some containers with holes for the pots. I got 75 and 150mm pots, I think strawberries in the small pots (4 pots per container) and chillies and capsicum in the big pots.

Nova

Hi Nova
Just got this topic from Jaymie. I start DWC this week. My fish tank is 17' X 5' X 6' with 3000 gallons. My grow bed is 40'L x 34.5"W x 11.25"H. I will use 2" foam floating on grow bed with mesh pots for the plants. Instead of the UGF I use a filter tank between the fish tank and grow bed. The filter is a 100 gallon stock watering tank. The water from the fish tank is upflow thru lava rock, then plastic (hi surface area) media, then a course, washable, fiber mat. Then the water flows from the top of the filter to the grow bed.

I think this works the same as yours, except the UGF is replaced with the external filter. My large rectangular fish tank would not accomodate a UGF. The filter has a bottom flush drain to clear sediment that settles below a grid the lava rock sits on.

I am in a cold climate and it will take a while to get my water warm enough to add fish. I expect your experience will help me with my system and I thank you in advance. You can watch my progress in my member system topic 'Dougs system in Michigan'.

I am interested in your plant setup. Hope you post some pictures of your plant containers.