Backyard Aquaponics
A place to discuss aquaponics

hi, i am new to aquaponics and i started to build a system with a capacity of 60 gallons, including my rafts and fish tank. my fish tank capacity is 35 gallons. so i would appreciate your help by telling how many tilapias can i have in my fish tank and how to not overrun it with fish.
and any recommendation is appreciated.
thanks

Have a read through the IBC of Aquaponics at the top of this page, it'll go through the basics you need.

But you need to work it off the amount of filtration you have, eg, growbeds.

So if you've got 25L of wet media, it'll be enough filtration for 1 fish grown to 500g.

Hi there.. Please give some more details as to how you plan to handle fish Solids... Filters... If so which? Do you plan to include media beds with stone or clay pellets? Just using Rafts means your plant roots will become clogged with fish Solids and then you will sit with root rot, as well as come to a point where Ammonia, pH and everything else will build up to points where you will need to drain water, thus no more Aquaponics... Just plain Aquaculture
Easiest way would be to design with GrowBeds in mind, at least one with about 2 wheelbarrows full of 20mm (3/4") gravel. Either an old bathtub, or build a wood frame and line with Pond liner, best might be the food grade IBC cut in 350mm deep tubs approach, and then planted with things like Chard, Basil, chat vessels, rocket, etc. From there then distribute the filtered and Nitrate rich water to your Rafts.
Doing it this way, you can stock with about one Tilapia fingerling per 2 gallons of Fishtank water
HTH

Sorry, but IMO that's definitely not a good method for calculating a system's safe fish stocking capacity N8Wulf.

Hi chrislot02,

It has very little to do with a system's water capacity. As Colum suggested, a system's safe fish stocking capacity is determined by the amount of bio-filtration contained within it.

Bio-filtration is provided by a number of different types of beneficial nitrifying bacteria, and other beneficial organisms.

The wet gravel in gravel filled GB's provides a large surface area for these bacteria to colonise, so the more wet gravel, the more bio-filtration, the greater the system's maximum safe fish stocking capacity.

Gravel depth is important, 300mm is widely accepted as suitable for most backyard type systems. If the beds are too shallow you won't be able to stock enough fish per m2 of GB, so insufficient nutrients per m2, so will start to run into nutrient deficiencies.

Just as an example:

A 1m2 GB, with 300mm gravel depth, flooded to 50mm from the top, will give 250L of wet gravel and be able to safely support 10x Trout, or 10x Barramundi to plate size (500gm).

The same 1m2 with only 100mm gravel depth and flooded to 50mm from the top, will give just 50L of wet gravel and only be able to support 2x Trout or Barramundi.

So 1/3rd the depth, but 1/5th the amount of wet gravel, or biofiltration (safe fish stocking capcity).

1/5th of the amount of fish per m2 of GB equals 1/5th the amount of nutrients per m2 of GB.

If you are going to run a DWC (raft) or NFT component off the system, I would recommend lightly planting your 300mm deep gravel GB's and running only 1m2 of DWC/NFT per m2 of gravel GB (provided you are only growing small leafy greens, such as lettuce, Asian greens etc, in the DWC/NFT)...

...or increase the gravel depth to 400mm in the GB's, stock with fish to this capacity and plant the GB's to full capacity, then for each 1m2 of gravel GB you can then also run 1m2 of DWC/NFT growing area without fear of running into major nutrient deficiencies... again, provided you are only growing small leafy greens, such as lettuce, Asian greens etc, in the DWC/NFT.

Anyway, once you've determined the gravel volume your system will have, you can then determine the approximate amount of water required in the system, this ratio is fairly flexible.

A gravel:water ratio anywhere between 0.6:1 (ie: single IBC system with 300L gravel and 500L of water) and 2:1 has been proven to work well, but the widely accepted norm is 1:1... This ratio gives a good balance of gravel to water, fish to water, and nutrients per m2 of GB.

Clear as mud???...

Hi again, well my system is a DWC without media. The water will flow from the fish tank to a swirl filter, then to a particulate filter with aeretion, finally it will be pumped to the rafts. I will have a air pump in the air tank, one in every raft and in the psrticulate filter. My plan is to recirculate all water 1 tiem every hour. But what keeps me worry is how many tilapias can i put in my fish tank that is 35" long 17" width and 14.5" high. And how to keep my tialpia population in control. This system is like an experiment to see if i could take this aquaponic to commercial size.

Thanks

Your fish stocking capacity is determined by the amount of bio-filtration you have in the system... What will you be using to provide the required bio-filtration if your system is DWC without media?

I think you mean the particulate filter for the bio-filtration.

And it really depends on what you're using for the particulate filter, and what it's surface area is. K1 media will have different properties to bird netting.

I think you should find a good book on aquaculture (timmons is the one usually recommended) if you want to go that route. There is more to it than fish/filter/plants. And very few of us on here are running commercial systems, and those that are usually won't detail everything for you.

For a backyard system with DWC, we'd just say put a media bed before the DWC, and that'll sort out your filtration, and cleaning the water for the plants.

UVI found that they didn't need an additional dedicated biofilter with their DWC.

Having said that ....

they did have netting as a particle filter and that would have had a resaonable amount of biofiltration capacity.
if you are relying on your plant roots to be the biofilter you CAN NEVER1 harvest all your plants at once.

1 Well not unless you harvest your fish first.

@Mr Damage: thanks for the lengthy and detailed information, I was working on previous info that stipulated something in the regions of 10 L per Tilapia fingerling. But keeping biofiltration Volume as more of measuring stick, makes more sense
[WINKING FACE]