Backyard Aquaponics
A place to discuss aquaponics

sorry VB, one could be forgiven for thinking it had not been written at the top of the page!

The further you get into aquaponics, the more you experience different systems, the more you get a feel for it.....

When looking at a design or listening to someones figures for a system, I might just feel like something seems wrong, can't quite put my finger on exactly what though.. Or stocking densities, show me a tank, and a growbed, tell me how much your pumping and how often, and what your expecting out of the system for harvesting planting etc, and instinctively I have a pretty good idea of how many fish would be ok..

You can try and sit down and calculate a figure, but with so many variables coming into play, it pretty much falls back to experience..

It's taking food production back to the days when thats what farming was really about, having a feel for the land and the cycles etc.. Yet with a modern twist..

I agree EB - I was about to post something similar. The best thing for people to do is set up a small system themselves and run the tests until they get a feel for what is going on. Suddenly everthing will seem so obvious.

First off thats made a bunch of stuff clearer to me.

Rup and Murray:
When ever I've read of "pushing" a system it has been in reference to maxing the fauna component either by way of the stocking density, feeding rate or often (strangely enough) both. A ratio of 1.5:1 (GBs:Ft)has less safety margin than ratio of 2:1 (GBs:Ft). I would imagine that the larger the GB:Ft ratio the easier a system would be to manage. At least in terms of avioding system crashes. You might have problems with the nutrient levels being high enough to get good growth but this could be managed by a range of additives that would be absorbed by the plants and wouldn't effect the fish (hopefully).

EB:
Right that explains a lot. I'd seen that 6kg:100L before and thought that it was a misprint or something. Now that I know more about Tilapia I can believe it.

So that ratio (as you say "guide" is proably a better term) was derived for Tilapia (I'm assuming since thats what I've read they grow). How does that relate to the species that we grow. 6kg/100L is around 1gk/16.6L. From memory it is recommended Baramundi can be stocked to a maximum density of 1kg/25L and trout to 1kg/20L in comercial recirculating aquaculture systems. I get the impression (could be wrong again) that most people on this forum are running their systems at much lesser densities than this. Yet people are getting incredible growth rates from their plants. Is this because they have less than 2:1 GBs:Ft or do omnivores and predators produce richer waste?

Apologies if I'm annoying people I'm just trying to understand. I'm doing masses of reading (spent a whole day going throgh the plants section of the forum gradually working my way through the lot) including this forum, RIRDC articles, DPI, Aquaponics Journal, etc, etc. Not just the AP stuff either but all the related topics such as worm farming, BFS, other flies, other larvae cultures, feeder crops, Greenhouse heating and cooling systems, the list goes on and on.

Having fun though

On a completly different topic had lots of fun tonight catching a Chalinolobus morio it was sooo cute!

Oh and I'm going fishing tomorrow,

Stuart - we cannot stock at the same sorts of rates as recirculating aquaculture because we do not remove water from the system to get rid of the nitrates and we do not run all the flash equipment like ozone filters and degassing chambers and god knows what else.

I think the ratios are a reasonalbe GUIDE (and guide only as discussed above) for our species also.

Stuart, i am also one who seeks to learn it all, unfortunatly with something like AP there comes a point where you need to "just do it".

You can read all the welding manuals you like, but the fact is that 8 hours of welding (with the right mentor) will teach you more.

Get in there mate, get your hands dirty (wet?) , test your ammonia nitrites and then when cycled your nitrates, and compare to feed rate and plant density................run a system for 9 - 12 months and see how it seems to mature and become near bullet proof...............

Ohhh. Step away from the computer for just a little while to chase a bat out of your house and look what you miss.

I was half way through that last post of mine when I couldn't write any more due to laughing so hard over the screams of my wife coming from the lounge room.

EB


A couple of months ago I read a book which I think was called "the Australian fish farmers handbook". One of the points the author made very strongly was that quality of feed in aquaculture systems is much more important than the price you are paying per tonne. Poor quality feed = more waste that has to be dealt with = more expensive operating costs. He went on to say that feeding your fish a carefully (even exactly) balanced diet that was species specific and age specifc was essential.

I'm guessing that in a AP system we just don't care. As long as the fish are fed enough of every thing they need (amino acids, vitamins, minerals, etc.) thats all that matters. As long as their not getting anything that will make them sick in abundance (like fat). Any extra is waste but that feeds the plants. Anyway I'm hoping so because I really don't want to use pellets. I can grow worms, BSF, slaters, yabbies, guppies, snails whatever in quantity but feeding them in a balanced manner to my fish, not just yet.

Agree whole heartedly. My system is virtually bullet proof these days. I spend 5 minutes at it on weekdays. Just enough time to through a few handfulls of feed in and look longingly at it wishing I could play with it instead of going to work

yeh, every day for the past month i've thought "i should really atleast check the ph".............and then another day passes...............

Stuart - it is not that we don't care - is more that we try to keep things as simple as possible. Getting the best quality feed is something we would all aim for. Most of us use pellets as the staple part of the diet - mainly due to convenience. There are severla treads here about alternatives and I like others hope to be making my own pellets before too long - as well as suplementing with meally worms, BSF, duckweed, Affrican Black Beetle larvae etc etc etc

I think what is key about 2:1 is that it gives a sense of scale. Knowing those numbers tells me that it would be silly to build a 20:1 or a 1:20 system for example. The important thing is to build what seems to be a reasonable system based on what we have learned here, and then carefully observe what it is doing. You might calculate that your system will support 17kg of fish, but as you learn the particulars of both it and yourself, you might discover that 15kg is a better fishload. Or 19kg.

Barra are commonly grown at 5kg per 100L in recirculating systems, and they have also grown at higher rates, I have read some rediculous figures in the past.

Yes, it relates to the protein percentage of the feed fed to the fish, it also relates to the amount of feed fed to the fish. Fish in commercial recirculating systems are there for one reason, to get them as big as possible, as quickly as possible, as such they are fed maximum amounts of feed.. The fish in my system are fed no where near the same feed per weight of fish in the system, because I don' want to just fatten them up, they are my fertilizer source and buy ing new fingerlings is expensive, I'll keep these for maybe a couple of years or more in the system on very low feed rates...

There are so many thing not understood about the complex relationships in aquaponics, things that don' seem right either.... I asked Dr Rackocy about the UVI system last year when he was in Melbourne, "don't you find that you have a lack of nutrients in your water once the water has travelled through 60m of plant roots and it's getting to the last plants before it goes back into the fish tank? Surely these plants at the end would suffer?" His answer was that the nutrient levels are the same at the end as they are at the start.... How the hell does that work..?

I've only just recently started to comprehend the idea that the water coming out of the growbed at any time is not clean as such, yes the bacteria has converted some of the ammonia over, and the plants have taken a little nutrients outbut it's still a nutrient rich coctail.

Does anyone know the effects of carnivores vs omnivors, vs herbivores in a system, and what if you feed your omnivor or herbivore the same protein% feed as your carnivor, will you get the same nutrient levels

Mostly studies into all these different aspects have not been done, people theorise based on known quantities, but most people are guessing... And then when you take gravel beds into account....???? The only person to have done extensive research into aquaponics with gravel beds was really Tom...

VB said:


But some people do. At least we have discussed that Tom Seperano did. 1kg/16l (6kg/100L) is a huge density. Imagine a 625g (plate size) fish in a 10L house hold bucket.

All the complicated equipment, with the possible exception of the ozone filter, that allow recirculating aquaculture systems to function is contained within the growbed. Steeve has pointed out that we don't want to remove the water and or solids (unless we have to in an emergency) like they have to do as a matter of course in RACS.

I know I only just asked this question but do the predators (eg barmundi, trout) produce more nutrients than the herbivores (tilapia). In land animals predator wastes are certainly richer but there masses less of them. Same with fish? Or does that hypothesis get completely mucked up when feeding them pellets?

Stuart

You have misunderstood Stuart. The fact is that recirculating aquaculture farmers stock at much greater rates than 6kg per 100 litres. Do a google and you will find some references to scary socking levels. This is what I am pointing out. I bought my tank from a guy who had been growing the same type of fish (jade perch) in a recirculating aquaculture system. He scoffed at the thought of only getting 6kg per 100 litres. I am not sure exactly what he was getting - but I would say at least 3 times that. The grow bed does not replace the method used by recirc aquaculture people - not to the extent that we can stock at the rates they do. The gravel bed is acting as a solids filter, biofilter and place to grow stuff to remove nitrates. This guy had ozone pumping through the tanks and degassing setup, in addition to the solids and biofilters. Also recirc aquaculture people generally run a lot of water to waste.

3 times you have got to be kidding. Thats insane.

Those figures that I had for the trout 4-5kg/100L were based (according to my source) not on the metabolic requirements of the fish but on their behaviour. Greater densities than that and they apparently freak out, stop growing pick up scaling knives and go nuts or something.

I've just looked at some of the info on Bara again and they were getting 8kg/100L by pumping oxygen into their systems. The only place I've heard of them using ozone was in the pathogen killing section adn that was in a document discussing the pros and cons of UV vs O3 sterilization of the recirculating water. Wouldn't O3 be poisonus or does it just convert to O2 by the time it gets back to the fish tank?