Backyard Aquaponics
A place to discuss aquaponics

i have 35 tilapia in 1700l. the water passes through 2 300l cut down ibc.s filled with expanded clay.From what i have read about the ssa needed for fish using grow bed filtration (25 litres/ fish), i havent enough grow bed volume. i intend to add earthworm to the grow bed medium.
i have read that an opción would be to include a mechanical filter. But the filter would remove valuable minerals produced by the earthworms metabolizing the residues in the grow beds.
i would be grateful for any thought from anyone

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You're right... 35 fish, with only about 500 L of wet media, is pushing the limits. But that ratio is a rule of thumb, not an exact formula.

I've managed a similar ratio for extended periods... main issue being high nitrates, which don't seem to have worried my fish or stunted growth.

And I believe that tilapia are tough.

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You could use a radial or swirl filter to remove some of the waste solids , there will still be some in fine suspension going to your growbeds .

Then you can use the solids elsewhere , worm farm , fruit trees ect , of course you can tip a bit in your growbeds you don't have to throw it all away , just manage it .

My next build will include a cone bottom radial filter which I can bypass if required so I can manage this issue , I have a cold season where my fish don't feed .

35 hungry fish and two growbeds means probably frequent cleaning of grow beds