Backyard Aquaponics
A place to discuss aquaponics

I am redesigning the SLO and filtration in our 2600 gallon system.
I've got a possible monkey wrench in the works.
For unknown reasons fish waste in the existing RFF is floating.
I've always used an Air-Lift pump to move the waste water up from the 5'6" deep tank.
Less than two months ago I started Skretting Classic Trout 3.5mm floating.

I have had that happen with Skretting Finfish Slow-sinking 6mm and 8mm as well as Zeigler Brothers Silver (can't remember size) at two separate fish farms I worked at. We always cleaned the RFF's through a bottom drain on a weekly basisy. Other than the fact that it looked kind of gross, we didn't have any issues as long we cleaned regularly. Our RFF's had a sort of skimmer set up around leading to the drain, I wish I had pictures; the skimmer increased the surface area of the outlet, so that a large chunk of floating solid waste would be less likely to slip out. Here is a link to a WMT prefab that essentially uses the same concept to give you a visual representation:

http://www.w-m-t.com/wmt-radial-flow-settler/


I feel like I have had the floating waste in the rudimentary RFF in my home AP tank (much less densely stocked) to a lesser degree while feeding Wardley Shrimp Pellets (sinking). So I am not really sure what causes it, but I am also not sure if it is anything to be super concerned about as long as it isn't causing clogs down the line or rendering your filter ineffective.

Hi,
Waste first sink at the bottom of the RFF. But after a few days decaying organic matter is generating gases inside the waste, making them float after a while.
You have to figure how long it takes for the waste to begin floating, and then clean your RFF before that happens.
For me it takes 7-8 days for thing to lift to surface...

I think this is probably because the waste that sank became anoxic/anaerobic - Some of the bacterial metabolic pathways you get with anoxic/anaerobic pathways produce gas like Nitrogen, Hydrogen Sulfide and Methane. The bacteria that do this are slower growing than their aerobic counterparts. It probably takes about two or three weeks before I see the solids float up because of gas production but it partly depends on how many organisms are left when you clean out the system each time, temperature, how much waste is accumulating.... I'd just scoop out the floaters with something (not your hands though).

It may also be that enough light is getting through to the bottom that algae is generating some gasses and causing part of this.

Thank you all. After reading here and inspecting the RFF I think you are correct about the gassing.
Today I'll weigh out daily feed quantities so we know how much feed is going into this system.
We have 100 Brook trout in this small system. I feed six handfuls twice per day.
Seeing some of the waste float provides another aspect of filtration I hadn't considered. This is good timing as I am designing my own versions of SUF & MBBR. It sounds like now would be the right time to design a mineralization tank too.
Currently the RFF is a 30 gallon barrel.
I'm finally feeling well enough health-wise to grasp what the correlations are between flows, filtration, feed and waste.
I'm so grateful for all of your compassion and explanations since beginning two years ago.

Flow rate varies due to conditions in filtration.
Waste also varies due to the amount of feed.

I should design this system to accommodate the maximum plus ~20% more of both, correct?

I struggled with the first since the beginning.
The second is the reason the waste in the RFF is floating.
The SLO and RFF are working well. How well is difficult to measure. What I gather from all this is I spent too much time fussing about the details.
The bottom line is the RFF was full after a week. The RFF is doing what it is supposed to do.
I need an easier way to clean the filters.
The main issue is the AP is in an earth-sheltered greenhouse which is sunk in the earth which in our case is limestone.
Going down further in the rock isn't practical around a 2600 gallon masonry FT.

I'll go ahead and make the new RFF larger since this should be easy to do using the barrel from the MBBR which has the bulkheads in the proper places.
The air-lift system on the dual SLOs lifts the solids up off the bottom of the FT well enough and the solids are not broken up. The ST is too high, but it is also masonry and can't be changed, I'll incorporate another air-lift to raise the water level between the RFF and new larger MBBR to keep the flow rate higher through the filters.
I'll reuse the current 30 gallon RFF as an off-line mineralization tank.
If I explained this well and it sounds right I should be able to create a pumped drain system to feed the mineralzation tank
Please provide feedback.
Sincerely,
Brian Rodgers

System should be designed for what the maximum grow out would be of your fish right before the day of harvest. (best case scenario)

Questions to ask to further think on......

What is current size of trout and the daily feed amount should 1-2% of that total weight (ideally - - obviously, that amount of feed will increase daily/weekly/monthly depending upon your individual needs and trying to achieve as they get closer to harvest.)

How does your 6 handfuls of food compare to the current size of trout? (over/underfeeding - if under, how would this impact design? (again, based on your specific end goals)

What is the current flow through your system on a hourly basis?

Typically shoot for 5 mins of retention time in a RFF situation. How does that compare to current flow with current and proposed upgraded design? (too slow/fast and how would either effect maintenance)

Cleaning/maintenance
Minimize solid bull up - net sock to screen larger debris for a quick cleanup. (prefiltration) easier to add to MT tank for breakdown but then Nutrient profile added back into the beds for uptake?

Cleaning-how often and how much time needed to do so?

My system is not ideal and these are things that I am trying to balance myself. I am not just noting things that may be just ideal/lacking b/c ultimately it is what works best for a particular individual.

So onward/upward and will help (if needed) in anyway I can.

On different note, please call so I can arrange a way to get cutter back if your done using it.

Adam

Hi all - great discussion here!

I'm in the process of building a small setup in my backyard - I'm planning to use a 60L RFF vessel (repurposed canoe water storage) on a FT of approx 750L. I have two questions that I hope an expert can help with:

1. would a small 20mm tap drain be OK for cleaning the waste on a weekly basis or should I cut out the existing bung and replace with a larger drain? and
2. would it be worthwhile installing a mesh 'skirt' between the stilling well outside and the main vessel inside to capture any smaller, floating particles, or will putting a fine mesh impede water flow too much?

Any guidance would be great!

Hi Bergo, the 20mm drain should be ok. You can always change it later if you want better flow. When I built mine I played with different types of shade cloth to finer filter, just add and remove pieces to get the flow right.

legend - thanks!