Backyard Aquaponics
A place to discuss aquaponics

The 2:1 growout pond ratio means for every 1000l of water I need 2 cubic meters of grow out beds for max fish density? This allows max 60kg of fish?

Has anyone tried seperating the tank with wire mesh so that you could have multiple stages of fish development allowing 1/4 fish harvest without effecting the garden growth. Or do you just stagger the harvest of plants in conjunction with the fish?

Matt

Hi Matt,

Yep, you've got it dead right, if you have a 2:1 ratio, with a 1000l fish tank, and 2000l of grow beds, you are able to have 60kg of fish, however, this is a 'maximum' amount, with that many fish you are at the very upper level where if one small thing goes wrong you could end up with dead fish. 40kg of fish in the 1000L would be a much safer amount, meaning that both the fish, and yourself aren't stressed....

I haven't tried sectioning of a tank as yet, but it is quite feesable.. After harvesting all the fish from a tank, if I don't have any more fish for a little while then I use seasol and fish emulsion to keep the plants going for a while until I get more fish.. Of course the bacteria levels will tend to drop a little without any ammonia to keep them alive...

My flood and drain with 4 growbeds, sat idle for about 3 months without any fish just recently, the plants in the growbeds survived ok, they slowed down their growth, but most lived for the 3 months on nothing but water cycling through the system...

Over time there is also a level of natural nutrients that build up in the grow beds, roots from previous crops being eaten by worms adding worm poo, old fish poo decomposing in the gravel, etc, this is all circulating through the system as well.

But then recently I stocked the tank with about 38kg of young fish, and replanted the growbeds at the same time. I was worried that the bacteria levels wouldn't be high enough to deal with all of the fish wastes but the system is doing very well, it's been almost 4 weeks now and I haven't had a single death, and the plants are starting to really boom...

Are there any suppliers of fingerlings you have managed to find over there Matt?

Joel

Joel - have you noticed much/any growth in your fish over the 4 weeks?

Thanks for you input - I am costing metal growout beds to compare with concrete. These wont be gal or stainless so I will need to paint them to stop rusting.

After furthur thought I realise that the size of pens would need to change as the fish grew. So I thought you could have movable mesh in a pie shape hindged in the middle.
I need to work these thing out as this will be a "business" (not for me)which will require carefully controls to max profits. Which will need to compete with locals who grow out tilapia in river systems without costs of pumps ETC.

Hey Matt,

In that sort of situation you probably want a brood tank, a seperate small tank where you keep your breeders that will be producing the fingerlings that will then go into your grow-out aquaponic system..

If your planning on using a growbed that may not be totally water proof, you can use plastic to line the grow bed. This is probably a good idea when using steel unless your sure that you've sealed the metal surfaces totally, some metals mixed with fish and water, well they don't mix...

VB, I haven't noticed any growth in the fish, but when you come out and look at them every day it's very hard to notice growth. However, knowing that they have a food conversion ratio of about 1.5:1, and that over the past 4 weeks I've fed them about 6kg of feed, I figure that as a group they have put on about 4kg.. Not particularly quick growth but it took them at least a week to aclimatise to their new surroundings and start feeding well

If I decide to operate a system with a low ratio, say as low as 1:5 grow bed to tank ratio - of course adjusting the number of fish in the tank to suit this ratio - am I likely to have problems getting enough nutrients to the beds. Will it mean shortenning the pumping cycles so that a greater quantity of water, and therefore nutrient (in his less concentrated situation) getting to the plants over a day. I intend to operate a flood and drain system and am dead against having to run continuous flow instead.

VB, Aquaponic systems are amazingly rezilient and adaptable. My system sitting under the verandah has a huge fish tank (2.4m dia) with one very small grow bed (1.2m dia). I've had between maybe 3 kg of fish up to about 20kg of fish in the tank at different times, and I find it very difficult to notice a great deal of difference in the plant growth..

When I grew a fantastic tomato plant that produced really well, in the bed last year , there was only maybe 3 kg of fish in the system. I figured that there wouldn't have been enough nutrients, but there was..

This one I do have going continuously, but I don't think it would make a huge difference if it was flood and drain..

How often were you thinking of having your system cycling VB??

I don't know what my cycles would be Joel. I would aim at having them at optimum intervals having regard to all the circumstances including:

- wetting the gravel at necessary intervals to ensure plants have the moisture they need
- cleaning the water sufficiently
- supplying enough nutrient to the plants

I am not adverse to using a timer on my sump pump as I would like to try and avoid the need to have a 2 pump setup and also I would like to be able to alter the cycle lenght easilly to meet specific needs.

I will run an air pump in my system as well. Will probably start seeking comment on those soon, as have been looking at the piston ones they have on ebay and will need to determine the best size to buy. I wouldn't want to go too big, as will probably try to run through trickle battery setup to cover fo blackouts.

If your going to have a bubbler as well VB, then this will allow you to adjust your cycling at will, without having to worry about the oxygenation so much.... If you have a grow bed with the same style of standpipe agrrangement as in the book, or like Murrays ones in his growbeds, this would allow you to have a great deal of flexibility in your cycles...

Stick a timer on your pump and you can play with all sorts of different time settings. Say, on for 15 mins then off for 30 mins, the growbed will fill up, then any excess water as the pump keeps going will drain over the standpipe and back into your tank until the timer switches the pump off. Then the water will slowly drain out of the bed, back into the tank, then after the half hour is up the pump goes back on and fills it again...

I guess it will depend on how long the water takes to drain from the grow bed, my large flood and drain beds actually take about an hour to drain completely before they are filled again, this may work out the same for you, if so, it means that your pump is only running for 15 minutes every hour, very efficient.... Basically in my flood and drain, as soon as the grow bed has drained, it will be filled again, so it's never without water for too long...