Backyard Aquaponics
A place to discuss aquaponics

I may have asked the wrong questions. I will start again. I have a rather new system (less than 4 weeks). I have 250 little tilapia (10 cm currently) in an IBC (950 ltr water) with water overflowing with inverted siphon (sucking water from the bottom of IBC) to a Radial Flow Filter (red bucket in the photo), which then overflowing to the biofilter (blue barrel), which with inverted siphon again, overflowing to the sump bucket (white bucket), and the water pumped back to the IBC via NFT system growing lettuce.


The biofilter itself is a blue barrel, filled with 2100 bioballs, and aerated with Resun aerator, pumping 4 ltr/min of air. Not enough to move the heavily packed bioballs though. The water from Radial Flow Filter is filtered through an aquarium sponge to remove small and light debris before entering the biofilter from the top. The water is removed from the bottom with inverted siphon overflowing to the sump bucket.




I am hoping not to invest much any more, as this project is overbudget as it is. And I really want to use the bioballs, which are expensive in my area, and considerable an investment for me. Is it possible to improve my biofilter further? Please help.

Thank you.

That sounds like way too many fish for the system to handle. But I don't know tilapia that well, so I don't know what they can handle, I think you're going to have problems when they get a little bigger.

Are you just running an aquaculture setup? Or an Aquaponics?

If it's AP, just add more media filled grow beds, the gravel (like blue metal/scoria/quartz) is exceptionally cheaper than the bioballs, and work the same.

I haven't done the computations to see if you have sufficient biofiltration, but what I'd be doing is making the fines filter completely separate to the bioballs filter, and adding more water to the bioballs and allow them to move in the water column and self-clean, ala MBBR.

By separating the components, this will ease maintenance, and each unit can be bypassed as required without having to shutdown the entire system. Filter wool, matting etc all clog quite quickly, so you're going to have to do very regular maintenance on your system as it is... look for ways to alleviate that burden, like by adding a larger swirl filter (cum settling filter), coarse and fine mechanical filtration etc.

Before doing anything else (if you haven't done it already), spend some time with a calculator and see what the stock capacity of the system is.

What are you doing about nitrates?

Its been said but 250 fish in 950 litres is a lot. At 10cm they are not that small either. Your stocking density is probably fine for an established system that is only going to house those fish for a short time before they are moved onto a larger grow out tank. However, yours is not an established system and you haven't mentioned your other larger system that is ready to take the fish once they have grown.

Have to agree with the majority on stocking ratio. Unless you have a lot of media/ biofiltration, that rate is going to cause problems. You have 1 fish per gallon, and at a harvest rate of 1 lb per, you could have 250 lbs of fish in 250 gallons. Well above the rates that most suggest. I have 40 fish in a 200 gallon FT, and they perform well, good growth- plants & fish. Better to be under then over IMO.

I have < 200 fish in 8000 Litres of water, the bio-filters are 2100 Litres of hydroton, 750 Litres of gravel plus 550 Litres bird netting, I think my system could do with more bio-filter?

Thank you guys, for the input. I am using the calculation of 1 pound of fish between 1 - 3 gallon of water. The major consideration that I have is that in my area/country, the typical harvesting size is 1/2 lb per fish. Way below western standard, but that is what is being sought after here. As it is considered as delicacies at that size. Calculating that size, it should be between 160 - 480 fish per 1000 ltr. Since my fish size currently is a lot smaller (20 grm per fish at the last sample, last Monday), I figure I have still a lot of space to go. Please correct my calculation if I am wrong somewhere. I understand in the west, the size sought after is between 1-2 lb per fish, but I will harvest the fish a lot earlier at 1/2 lb size.

I am running AP. After the biofilter, the water is pumped through an NFT system (no media, only gully with very thin water), about 1 m2 growing area.

Considering all that, I am seriously considering of turning the system to trickle filter using the same bioballs. What do you guys think?

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What about an anaerobic sand bed to convert nitrates to nitrogen...

[url]....http://www.wetwebmedia.com/deepsandbeds.htm...[/url]

This explains why I have managed to keep a Cichlid aquarium alive for many years, without any water change..
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First of all imperial sucks for these sort of calculations.

Second that is a stocking density of up to 120kg/m3

That is going to end in tears unless you start using pure O2.

Tilapia can handle much higher stocking densities than we are used to but even so with only aeration (as distinct from pure O2 injection) a theoretical maximum density is 60-70kg/m3.

Thank you, guys. I think I better reposting part by part of my system for evaluation. Since I may have understand it wrongly. May be, then, I can see why my system has me working a lot more than I think I should be for it.