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So I had been using a filter made of window screen made for pet claws. I ended up with tilapia in the grow beds. Got them out, more fish, got them out, more fish. I don't know if eggs are getting through or if somehow eggs have been hatching from the previous batch that I got out that somehow survived without the mother.

I'm building new fish tanks. Going from two 6 foot round, 2 foot deep tanks to 4 foot by 8 foot by 5.5 foot deep tanks.

I'm wanting to put in a radial flow filter but can't find  information on proper sizing for diy. I see one place that says retention of 2 minutes, and everywhere else says can't be too fast but can't be too slow without any word on how to properly size one.

What is the best way to make sure no tilapia eggs get into the grow beds again? I've lost way to many crops due to the tilapia

752sq feet of grow bed trying to make small scale commercial work to test the market.

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Hi Devoid

Is your growbeds media filled or dwc?


DWC, they hatch in the grow beds and eat all the roots.

Consider adding a few bio-filters (growbed filled with media and worms) between fish tank and DWC - the fish poo will then be break down by worms - you can use a screen at the input to capture eggs/fry.  If you use worms you''ll need to use an eb/flow system to allow for oxygen - this oxegenated water will also benefit your DWC.

I've recently swapped my radial/swirl filter for a bio-filter - it is unproductive volume.

Unproductive volume? The radial filter is to remove the heavy sediment so it doesn't clog a media filter. I'm pumping 15 gpm through each of 4 fish tanks. No time for ebb and flow.

In my opinion the longer time the better for a radial filter. If you have a preferred time just multiply GPM by however long you want to delay the flow,i.e. 15 gpm x 2 minutes = 30 gallon filter. I have a 600 gallon system with and adjustable pump so I pump half the water through the GBs and half through the FT. to facilitate extra ammonia/nitrite filtering. 

Murray says if it's too fast it won't catch much. If it is too slow then it only functions as a settlement tank which would need much much longer time. Unfortunately he never mentions a good flow rate for it.

The only number I've seen anyone say is 2 minutes and only one place lists that.

Unless I'm mistaken a radial flow filter is a settlement tank. There are lots of videos on radial flow filters on YouTube. Check out this guys videos.  I enjoy all of his stuff.

Radial flow and swirl filters are solid separators.

Settling tanks would be at least as big as your fish tank to hold water for an hour. At least that's the number I was seeing in previous research.

I tried to find where I had seen it but I'm pretty sure you don't need to hold the water but just a few minutes. Most radial and swirl filters that I've seen are 5 to 40 gallon units. Mine is a 65 gallon pickle barrel but I only use about 2/3 of it. Not everything settles but a huge % does. The rest is broken down in the GBs by bacteria and red worms. If you have worms in you beds you have the best worm farm you could ask for. 

I'm using deep water culture rather than grow beds. I'm looking at going small scale commercial to start with.

I want a 65 gallon barrel full of pickles. I really want pickles now and have none :'(

You'll need a complete filter set up. Check out

Got this info from the first video.

The formula I use to see how long the water is retained in the filter before moving on is:
Size of filter (in litres) / flow rate (in litres per hour) = Retention time in hours. 
(Same can be done in gallons & gallons per hour)
For our system the equation looks like this..
50 / 2700 = 0.0185 of an hour or 1minute 7seconds
To help you out here is a handy Decimal to Time Calculator

Hope that info helps some out there interested in setting up a solids capturing RFF..

Also this is a good video:  or

The question is what is the ideal retention time for a radial flow filter.

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