Backyard Aquaponics
A place to discuss aquaponics

measure a couple of liters of water on your scales. Then put your goldfish in them and find the new measurement. This will tell u how much your fish weigh.

or if you don't have scales, use a jug with small scale on the side ie goes up in 100ml lines and put a litre in. Then add some fish, see how much the water level rose, divide by the number of fish and that will give you an average weight. (as far as I know, fish displace about their wight in water)

Monya, that calculation would give you the volume of the water that was displaced, ie the volume of the fish. Beacause the density of the fish is not the same as water I would suspect the results would be fairly inaccurate. Thats something someone can work out.... what is the density (grams/ml) of a goldfish and a silver perch. Use the first method to work out the actual weight, then use monyas method to work out the volume and hence calculate the density. Another example of Aquaponics used in schools. I have a gold star for the first correct answer!

7.3

7.3 ? That was fast! or is that just a guestimation?

TimC- Monya's method should be fairly close. Fish have fairly neutral bouyancy, or they would have to constantly be fighting to maintain their position in the water. They have the swim bladder to slightly alter their bouyancy, but they should displace their weight in water within 5%.
When fish die, they no longer regulate their swim bladder, and as rigor mortis sets in, they will often float.
Measure their displacement, then convert ml to grams, and you have the answer within 5%.

I flunked math.... Let me know when you have an answer. Better yet, I like using the scale better.

Is there such a thing as goldfish scales?



Of course there is, you find them ON THE GOLDFISH !!!!!!!!!!

My goldfish don't want to be weighed , their FAT and PROUD !

Hi everyone I'm Kyle from Zimbabwe my question is there a formula to work out how many kgs fish per litre of runing water to plant population?

Hi there Kyle the formula often used doesn't take into consideration the plants or plant density and should probably. This is especially true for flowering/fruiting types. If you plant to many they will starve for everything but nitrates it seems. So they will grow quick but not produce. Leafy vegetables however you might be able to plant very heavily.

Somebody correct me if I am wrong.

Dan, the "formula" used growbed size to infer planting density, its gon a little awry with nft pipes and the like.

Kyle, i'd say use the 60kg fish to 1000 liters fishtank to 2000l growbed space (at 30cm deep) as a MAXIMUM. Then play with the figures.

There is heaps of discussion on this topic, if you're luck one of the smarter moderators might link to it

If you're going to use nft pipes, then you could woirk out roughly how many plants you could fit into a certain liter growbed and work with the figures that way.

Ultimatly Dan is right about heavy / light feeders and nitrate testing is invaluable.

Hope we haven't confused you too much on your first post.

If we have then type up what sort of AP system you're thinking about and the size of the fish tnak you want to use and we can help give you some figures.

Hi Kyle and welcome to the forum,

difficult ques to answer:

we have generally steered away from this due to so many variables
leaf or fruit veggies
fast or slow growing (celery ~22 weeks, lettuce 6-8weeks)
space required for a particular variety

The standard ratio that tends to be the norm here is:
100 litres of water or 200 litres of media will support 6kg of fish weight

Have you got a system running yet

Thaks that helps a stack. no I only just decided to stick it out in Zimbabwe, we've had a bit of a rocky 6 years. I'm thinking of a 12500ltr Fish tank with 3 Ha green house but am worried about starting too big. whats a good start up size but still ecconomical?

Hi Kyle,
Welcome!
Folks start out with anything from a 30 gal aquarium, to their un-used swimming pool. We need a lot more answers before we can recommend anything And btw, folks here don't think anything is -too- big, but for large projects, we would probably recommend a stepped approach, and perhaps a prototype.

What are your goals? Feed the family? Feed the village? Raise enough basil for your pesto-passion? Raise leafy greens, or gorgeous tomatoes?

What can you get easily? 55gal drums? lumber? pond liner? raw clay? PVC pipes? stock troughs? bathtubs? gravel? lava rock?

Holy smokes....a "Ha" is a Hectare, isn't it??? I just realized that. So, like....7.5 acres. You aren't fooling around, are you?

OK, one thought I have is that the 12500ltr tank would certainly be your final grow-out tank, but you might well need smaller tanks to grow out the fingerlings. What about starting by building the greenhouse in sections, with smaller set-ups to use as fingerling growout tanks?

Thanks Janet because 99% of the commercial farms in Zimbabwe have benn taken over by other people. I am in the fortunate possition where I can pick up any ex farm equipment for next to nothing. I'm trying to make good out of bad, whats in my heart is to produce big quantities of food, my immediate markett is around 10 million peoples daily food requirements. I know i won't make it in one day but i need to start somwhere.