Backyard Aquaponics
A place to discuss aquaponics

I am interested in ensuring that the fish and the plants get the nutrients required to make them a beneficial food to eat. At the same time, I want to make sure that the inputs are as organic as possible and are also sustainable (and economical e.g. duckweed).

I am sure research has been done on this. What are the commercial aquaponics growers using for fish food and do they supplement outside of this.

I know Joel has discussed in the past using wheat, sprouted wheat and egg as a food recipe. Does something like this have all the stuff needed in it and if so what is it that it has?

Would duckweed on its own result in a nutrient deficiency, or does it in turn depend on what you feed the duckweed?

In another thread we discussed adding egg shell etc to our growbeds etc...
I know that there are loads of the all precious trace elements in the oceans, so I intend to add sea shells to my gravel... but as a quicker fix I am adding cuttlefish bones - I got 3 good sized ones from Overflow for $1.50 - they go into my system tomorrow

I am adding a liquid chelated iron supplement to my water, it has other minerals in it too (I'll find out and list them). I'm a bit foggy on it but my understanding is that the chelated iron can be uptook by the plants readily.

I am also going to look into rock dust, ala this article (I want to ask the landscaping store folks about their opinions of products like Planter's II):
http://www.championtrees.org/topsoil/bioponics.htm

I added some (just 3) 6 inch sized nails at the bottom of my lowest tank, right where the water flows in - hopeing I get iron from this (It was a spur of the moment laps of insanity)

Bloody good question VB.... Something I was contemplating just the other day with my barrel system. I planed it to be totally self supporting once it's up and going. To begin with I have the worm barrels with manure and compost in them, this will supply lots of nutrients as they are fed to the fish, but over time as I remove fish and plants from the system, unless I am putting them back into the system again then the system is going to run out of some nutrients and minerals.. I'm going to have to get a biodigestor happening so that I'm not flushing my nutrients away...

So far as the short term nutrients in plants, not so simple, there are so many variables.. I'm not sure how much work has been done in this area, I know that the feed recipe you mentiond had a breakdown of what vitamins and minerals were in it, I'll look it up in the morning, got to discover what issue it was in again....

I'm interested to hear other peoples thoughts on the whole subject...

A touch of aquarium SEA salt, the one used for marine aquariums, wouldn't go astray, as it contains all the trace element of the ocean as its produced from sea water.

There is another product, my soon to be brother in law got 20 litres of this "gravel" might have been volcanic, cant remember, but it was to be mixed in with his dirt for his veggie patch, apparently very high in macro and micro minerals.

VB, IMO this is what you need to worry about. The plants can "make" all the vitamins that they are known for ie: vit c for citrus. But the minerals need to be there for the plats to take up. It always makes me smirk when i see veggie X has so much mg of calcium. Is this quoted from one piece of reasearch? The mineral quantity of the mature plant will be wholy dependant on its availability in the soil, more so for the micro minerals. So this is what i'd be looking into. I'll try and find the name of that volcanic gravel, might be a worthwhile addition to the grow bed. But i'm also quite sold on the sea shell idea, maybe even the sea salt.





I might be wrong here, but although shells are orimarily calcium carbonate, i'd be very surprised if many of the oceans trace elements were not contained in them as well. Don't forget, we're talking about TRACE amounts, usualy in the micro grams.

Food for thought anyway

Steve

It seems logical that we would have to 'help' with the nutrients and trace elements to some degree at least! If we dont make sure that they get added somehow, where else would they come from? the grow bed media???

Maybe something like this? http://www.orchidimages.com.au/product.html
the rock mineral packet ? added to the growbed gravel ?

Micro-nutrients are all important in their own roles and distinct lack of one thing can cause lockout situations with other micros and even macros.

Iron supplementation is common practise with chelated iron however there is an alternative. Feeding your fish in high iron veggies will also add available iron to the system. As pointed out, low iron in spinach = low iron input doing it this way.

Fish food today is processed with added micro-nutrients (normally fish meal) and vitamins creating a wholly balanced diet (just badly balanced maths to make it)

Adding sea shell will also add a lot of Phosphorus. This is ok should you need it. If you don't need it you may buffer your water so well with carbonates you'll be unable to shift it without a concerted and lengthy effort. Phosphorus is also found in high levels in fish food. If you lack algae eaters and add seashell you may very well regret it and spend a lot of time mowing fields of filamentous algae.

As we learn, I'd advise you to supplement regular fish food untill you are sure the micros, macros and vitamins you need are available in your organic food sources. I think moving away from fish meal is important, but safety of fish is paramount.

Feeding crushed shell as grit in other foods to worms is another ball game. This should be done in very small doses. The resultant castings tea will be high in every trace element. Again, watch your Phosphate levels. This tea will make daphnia and brine shrimp populations explode. These Daphnia and Brine shrimp will also be very high in micros.

Certain plants strip phosphates better than others, and could keep levels down. These warrant investigation but that's another subject.

For algae eaters it is important to add some wood to your tank or pond for them to suck or chew on. If you are producing micros via shell this will also encourage single celled algae that are valuable plant waste removers.

Sounds like finding inputs may not be the difficult part - it is getting the balance right that is the challenge. How do you know how much of an input has been taken up by the plants/fish and how much is still in the water? (that was a retorical question)

Something that occurred to me after my post last night is that feeding fish (and/or adding to the water) plants grow from my normal garden may be the solution particularly if I continue to keep my soil very healthy by adding composts, manures, green manures etc. There are various herbs and other plants that accumulate specific elements - e.g borage & yarrow. This of course depends on the elements being available in the first place. Question is whether fish will eat the stuff (even if incorporated into food) or whether it would do any harm if cycled through the water (smallish amounts added as a liquid tea and cycled through the system).

Is there any easy way to know whether plants are getting the minerals that are beneficial to the consumer - does a healthy (and perhaps tasty) plant indicate that it has the right stuff? I suspect tast and health are indicators.

Good questions. All of them.

Now don't get me wrong here, I think sea shell is an obvious and easy solution to the problem of micros. Just balancing this with algae eaters and a bit of wood/driftwood (which will also slow the pH up effect of the shells) is, IMO, a smarter approach.

Now - the rhetorical question - How do you know how much of an input has been taken up by the plants/fish and how much is still in the water?

A figure of 0.6 sq metres of plant growth for 1 kg of carnivorous fish has been given in research. Unfortunately the feeding rates weren't given.

This is still a fairly safe estimate to ensure the plants are removing the systems wastes as they are produced. The figure was also given for lettuce, and so the area of plants needed may be reduced when introducing heavy feeding plants like tomatoes and cucumbers, legumes, etc.

Manufactured fish foods have the correct balance for Aquaponics. Some systems still need chelated iron, some other trace elements, this is due to a lack in the source water, rather than the food as water itself contains many trace elements.

Moving away from fish food to more organic sources may well swing the nutrient balance. As source water differs in mineral content so does soil in differing areas. NZ soil has problems specific to NZ etc.

Growing from the land and adding organic inputs works in theory. And should work in practise. Knowledge of your local soils strengths and weaknesses and addressing these as an organic gardener and you are well on your way.

However, you now have two gardens, why the Aqua?... Not so practical or feasible a solution... But it is a solution.

The largest exports of micros will always be your fish. If they are floaters, put them in the worm bin and send the micros back.

I think a varied diet is the way to go.

All good info! keep it coming, AA you raise some good points to keep in mind.

I think the main thing is what ever approach you use, do it in moderation. You are correct in the buffering capability, and at equilibrium i think calcium carbonate buffers to 8 or 8.5 which is too high. moderation is required. I know test kits are a contentious issue, but GH and KH are also easy to test for. RE phosphates, definatly an issue with algae if you have too much, but often it can be lacking in a closed loop.

Whats did people think about the mineral rocks in linked to?

AA - For me personally aquaponics will be an addition rather than substitution for my conventional fruit, vegetable and herb gardens. I realise that for a range of reasons not everybody has this luxury. I am fortunate in that I have sufficient space to do this, the climate (in the most part) and my soil is pretty good (mainly due to me using permaculture practices in my gardenning). For this reason the use of conventionally grown plants to feed fish and/or add nutrient to my aquaponics system is a real alternative. The challenge will be identifying what works without killing the fish .

Steve - My chooks got eaten by foxes a while back and i am in the process of doing a reno on the pen that will stop any repeat of this. I will then get 20 new chooks. I used to use the Ridley pellets. I am hoping to reduce the reliance on commercial pellets by free ranging them more and supplementing with more scraps and things I grow in the garden for the chooks (like leaf amaranth).

I would be reluctant to add chook poo in any form to the aqua system, but I guess the plants that I grow in the garden that have been fertilised by the chook poo will have all sorts of trace elements available to them due to the supplements in the pellets. I can then use some of these plants to feed the fish/add to the system.

Nobody has commented regarding the suitablility of adding teas made from appropriate plants into the fish water. What do you all think. Also, what do you think about adding compost tea to the water to release nutrients (would have to watch out for algae problems here).