Backyard Aquaponics
A place to discuss aquaponics

Good day All,

I started my backyard aquaponics system October 2017. Since then I've cycled my system without fish over a period of six weeks, added fish and grew a few plants. Ive got a split flow from the fish tank to a media bed filled with gravel and to a DWC container. Although ive seen good results from the media bed, Ive been struggling to get the DWC to produce any good results, no matter the type (lettuce, kale, rocket, basil). They all seem to have leaves turning yellow and eventually die a few weeks after being transplanted into DWC. I also noticed a strange slimy substance grow on the roots. Hopefully this is not root rot or pythium. I have 80L plastic container with aeration provided by a 210L air pump with 2 air stones in the DWC container and recently added a swirl filter before the DWC. It is especially strange since the plants in the media bed are flourishing while connected to the same water source, so i doubt there's any disease in the water. I also noticed red wrigglers and other black worms (which i believe to be moth fly larvae) on the plant roots in the DWC. If anyone could help me solve this mystery I would be so grateful. I've added more details below.

Fish tank
800L capacity fish tank, currently filled to about 400L
30 male Tilapia (40 grams/EA)
1200L/h water pump, max 2.5m head height
400L/h air pump, 2 air stones

Gravel Bed
160L plastic container
Loop siphon
Time to fill: 20 minutes
Time to drain: 5 minutes
Plants in the gravel bed grow well.
1 broccoli, 5 cherry tomato plants, (removed the lettuce which bolted due to summer heat i suppose?)

DWC Bed
I used to have a 160L container with styrofoam raft but replaced it with a smaller 80L container with holes drilled into lid. I didnt like the styrofoam idea.
80L container
constant flood
210L/h air pump, 2 air stones
flow rate approximately 80 L/h
Swirl filter added to minimise dirt ingress to DWC.
Not sure what the brown stripes are on the sides of the stand pipe and container? They are also visible on the plant roots.

Water Quality
Temperature ranges between 20 degrees C to 28 degrees C in summer
Ammonia 0
Nitrite 0
Nitrate 50-200mg/l
PH 7-7.6 (depends on the day)
General Hardness 16 dGH
Carbonate hardness 15 dKH

Hi Franci

Have you tried some new plants since adding the swirl filter , any improvement ??

DWC needs the cleanest water you can get and good aeration

Water going straight from your fish tank to the DWC is likely the root of your problem , Fine particles of fish waste coat the roots and starve the plants

Also make sure your airstones in the DWC are up off the bottom a little so they don't continually stir up sediment

Perhaps slow your flow rate through the DWC down its only a little container this may be continually stirring up the bottom

If your not getting settling sediment in your DWC something needs changing

I ran a small DWC made from a cut down IBC and it was remarkable how often it needed cleaning , I think mostly plant root fragments , I had a tomato plant once with a hanging root mass of 6 foot long when I pulled it out.

The tried and proven system is water through a media bed then a setting filter of some kind then your DWC then back to fish tank.

I would add another media bed (constant Flood) then your swirl filter then your DWC run this pretty slow flow rate

Just rig up something to try if it works for you then just redesign your layout

Aim at getting your plant roots "White"

Cheers

Hi Terra

Thanks for your feedback.
I have tried new plants since the swirl filter but they've not faired any better. They still form this slime on the roots.
My air stones are in the bottom of the dwc do yes they may be kicking up some sediment. I will raise then off the surface as you said. I will also try to improve my filtration as well.
And slow down the flow rate into the dwc and clean it out as soon as I see any excess muck inside it.

I tried using some pool noodles as a type of grow media instead of net pots now the only white roots I have are those growing through the blue noodles.

Regards

You could also raise the media bed so it drains into the SF then into the DWC then into a sumptank for pumping back up to the media bed.

The brown streaks look like they could be made by fly larvae. Basically the larvae live inside a tube and you're seeing the tube. Occasionally you may see the larvae pop out if they are still present. I think they are also called midge larvae or Chironomid larvae and look something like mosquitos when they hatch but they don't bite. Another possibility is that these might be structures for a tube worm of some sort.

Hi Pete, Scotty.

Thanks for your feedback.

@Pete, yes ideally I should have done something like that from the beginning. I thought i'd try to make the setup as simple as possible, without the use of a sump tank and swirl filter. And that I could control the waste entering the DWC via some mechanical means like a cotton/pond filter material on the inlet to DWC. Now its clear to me that much more needs to be done in terms of filtration. In fact there are many aspects of my setup that could be improved upon. If i were to expand this setup at all there would be a major redesign (FT>swirl filter>sump+pump>grow beds. Hopefully I can get this to work with a bit more tweaking. If it shows any sort of improvement it will be good motivation to start the redesign process. Then again if no I have no choice but to incorporate your suggestion. But for now I really don't want to cut into the fish tank or raise any feature requiring a higher pumping head height if possible, as i like to keep the grow beds above the fish tank due to space constraints, unless required.

@Scotty, Yes!! I have noticed larvae in those brown strips. I thought it was actual solid fish poop straight from the FT. But then thought how could so much of it get through the swirl filter? I also thought the larvae was just eating the "poop" that got into DWC and settled on the roots. I have also noticed a couple of midges and moth flies hanging around the dwc. So yes, you're right. Just not sure if that is related to the slime on the roots. I've subsequently read some threads about using smaller fish like guppies to control this problem. Hopefully this solution wont create too much solid waste in the DWC. I've since been draining the SF much more regularly, and reduced the flow rate and raised the air stones off the surface as mentioned by Terra in a previous post.

Regards

I'm grateful to read the others knowledge regarding DWC, I've never tried it

You can also run water into one catchment and then over flow into multiple containers and have the last one DWC with cleaner water after settling in the previous containers