Backyard Aquaponics
A place to discuss aquaponics

since ive got your attention i should fire a question quick - I am a renter so i need my system to be somewhat portable hence i need a light weight GB medium - expanded clay is sooo expensive and i cant get a hold of scoria so do you know of anything else that is light(ish) and cheaper than expanded clay?

Has anyone used diatomite?

its the best stuff for raising cuttings. amazing root systems
squats all over perlite and vermiculite

also aka
maidenwell

http://www.diatomiteusa.com/

http://www.earthlyworms.com.au/products ... cts&sub=10

http://www.hotfrog.com.au/Companies/Mai ... -Australia


i use dto get amazing root growth with rooting cuttinsg using IBA in pots of this sitting in water
the osmotic pull of this stuff is excellent
so flood and drain systems might have to be adjusted to a lower frequency?

but you can buy all different sizes graded. the larger grades would probably be excellent

well..
i have a bag

ill have to put in a bed...

One of the forum members (The Hopefuls) uses Maidenwell as a growbed media...

And it's used extensively as a seedling raising mix in commercial hydro....

Only down side is it's pH can run to 5.8...

the hoefuls have had to constantly buffer their system to keep it around 6.4 - 6.8 ....

Hi All

Sleepe mentioned that pea gravel will reduce the available phosphorous in the system for the first few years, this was my preferred option as I can get a trailer-load from 'Soils Ain't Soils' for $80. This is in contrast to expanded clay - that $80 will only buy me a few bags from Bunnings.

How do you manage your phosphorous & if you are able to establish that it is a bit low could you add a *small amount* of compost tea from chicken manure?

Mollison (Permaculture) was a fan of running ducks next to his natural swampy type aquaculture systems... does the principle transfer to AP, or is it too risky?

there are some members doing Duckaponics. There theoretically is some risk in using warm blooded animals like ducks and chickens etc for aquaponics because of the possible pathogens they could introduce to the systems, however there are some people doing it.

As to the comments about pea gravel locking up phosphorus, I suppose it might depend on the exact type of rock that the pea gravel is made of. Pea gravel usually refers to the size of the gravel not the type of rock it's made of. Limestone or marble pea gravel should be avoided due to pH issues. I have had no problems with quartz type river rock pea gravel though.

I've been using river rock of a size that many would call pea gravel and I have not noticed any signs of phosphorus deficiency in my plants. Plenty of flowering and fruiting when temperature conditions are right.

AP systems tend to be very high in Nitrogen and phosphorus so a little phosphorus binding might not even be noticed as the levels are plenty high to keep the plants happy anyway.

Hi everyone, like many others before me i have decided to take up koi and goldfish keeping.

I just turned my 40,m^3 pool into a pond and built a 1.5 cubic meter biofilter. however my main concern is if i use 1/2'' gravel like many have suggested will the weight break the pond liner that i used to water proof the biofilter? it is basically a 2.4m*0.9m*0.6m (L*W*H) hole in hard clay ground with the pond liner in it and bricks around the edges to hold the pond liner in place. so ultimately my concern is will the heavy weight of the pebbles cut the liner against the hard clay or stretch it too much?

thank you for your help

Bill

ps. just thought will it help if i used a layer of sand at the bottom to "cushion" the hardness of the rocks or if i should the clay under the liner by wetting it? or am i worrying too much.......cheers

Hi Bill, and welcome... we advise NOT including sand/gravel/pebbles in the fish tank/pond...

They merely act as waste traps... furthering anaerobic breakdown and water quality problems...

You could use gravel in a growbed situation... which also acts as a bio-filter...

But I don't think that's what you're doing or proposing... perhaps some pics would assist us understand...

Sounds like they are talking about using pond liner to line a hole in the ground to be a "biofilter."
If it is a high quality/heavy duty pond liner, then I wouldn't worry about the rocks cutting the liner (at least I've used 1/2" river rocks in lined beds using the thick EPDM liner and the rocks never hurt the liner.)

However, I'm not quite sure how you are going to make a gravel filled hole in the ground work for you as a bio-filter. Perhaps you need to make a system thread and expand on your design ideas with pictures to help us understand what you are planning.

Hi fellas, thanks for the quick response. I guess my original post wasn't as clear as I thought it was.

So basically......the pond itself is a 30-40cub meter pool conversion. Next to the pool I dug up a hole of the dimension 2.4m*0.8m*0.5m(L*W*D) which I hope will serve as a biofilter. Then I placed a sheet of Pond Liner in the hole so that it is water proof. I have a 6000L/hr pump pumping water from the pond into the bottom of the biofilter then the overflow simply cascades back into the pond.

So my understanding of a biofilter (with some sort of bacteria) is something that get rids of all the harmful stuff such as NO4 and NO3 etc and the water plants obsorbs excess nutrients so that algea growth is controlled. And from my understanding, the gravel etc is only there so that the bacteria colonies and grow on it.

Please correct me if my understanding is not correct.

Any help and advice will be greatly appreciated.

Bill

ps. this is before i put in the liner and built the brick wall around the top edge of the hole. i will upload a better pic tomorrow when the damn rain stops ..... cheers

Hi Bill... what you're proposing is essentially a form of wastewater treatment... and/or reed bed type system...

While such a system will certainly act as a "settling" trap for suspended solids and perform some nitrification...

It runs the risk of becoming clogged over time... and/or developing anaerobic zones... particularly if it isn't oxygenated...

Pumping into the bottom of the gravel filled pond isn't likely to provide sufficient oxygen IMO... to prevent anaerobic zones forming, particularly as the "sludge" builds up.... and the flow back into the pool may not provide enough oxygenation for your fish stock...

My other concerns are that with the "bio-filter" sunk into the ground... you can't control run off... and possible contamination during high rainfall events...

Also, should the sludge build up significantly... it would be very difficult to clean the "pit"...

Also exposing high nutrient water to sunlight is likely to in fact promote an algael and moss growth on the surface of the gravel... depending on flow rate...

I'm not sure what sort of plants you're aiming to grow... but while it may work with reeds, bullrushes etc... I doubt that it would work with vegetable produce... again due to lack of oxygenation...

In "traditional" aquaponic growbeds... we use a "flood & drain" method... both to provide oxygenation and bio-filtration...

What you propose may well work for low stocking density...

Hi, thanks for your reply. I now have a few questions,
1. whats a flood and drain method?
2. why do u think that this will clog up easy? I read up somewhere that one of the advantages of gravel is its porosity, as in water can flow easily between the rocks.
3. also, i have 2 small Koi at the moment, what food should I feed them? Currently they are eating the algea and insect lavae I think.
4. if, and when i have the biofilter filled with gravel, should i plant on the edges only or is it ok to cover the entire biofilter? The reason for this is does the bacteria colonies need sunlight?

Thanks

Bill

What's your "fall" height of your cascading waterfall ... and length of return to the pool...

Depending on fish stocking density... your pump rate might not be turning over sufficient water volume to provide oxygenation and/or bio-filtration...

With only a few Koi... in that size pool... none of the above is probably going to matter... other than the eventual need to clean the "filter"

Hi,

The fall height of the cascade is only about 20cm.

Ultimately I am hoping to plant some lotus and lilies in the pond and some decorative plants in the biofilter. After reading your posts, I did some research into "proper aquaponics" and im fascinated by its efficiency. I reckon once the pond is in stable condition I might build a couple of experimental grow beds with chilli plants, but this will be a project for my next uni break hehe.

In terms of stock level, will 20-30 koi sized fish be considered heavily stocked, medium stocked or only lightly stocked considering the size of my pond.

I presume that the fish is fine feeding on natural stuff now, but if their number increase I reckon natural food source would not be sufficient. I did some research online but alot of them are ad's and commercial food promotion..... some said cabbage, brown bread etc?

hmmmmm......... I never thought fish keeping could be so complicated but I guess thats the fun in it.

Thanks

In that sized pool 20-30 koi should be fine... depending how your filtration and oxygenation pan out longer term...

In terms of feed... if they're feeding on natural feeds... then the population will only grow to the level of available feed... but you should be able to source Koi feed from somewhere... you just might have to pay for it...

20-30 koi in a 30-40.000 liter system is very lightly stocked. They will produce ammonia, but because you've got so much water it will be very diluted. Plants would grow a bit slower than in a "higher load" system. But since you don't want to feed a lot, and grow mainly decorative plants, I suppose that's not much of a problem.
I have 5 big koi and some 15 smaller fish in my own 2.500 liter (total) system, and I consider it a medium "load".

Koi eat just about anything. I know somebody with a koi pond that just throws all his (organic) kitchen waste into the water and the fish really thrive on it.
They don't eat beans, peas and corn though; they just can't digest the 'shell', but if you have lots of those you could sprout them first.
They do eat bread, but it shouldn't be more than a quarter of their diet IIRC, and white bread can contain some mild bleach substance that is harmful for fish.

Also, since you have a big pond area for the amount of fish in it, you might be able to grow duckweed or azolla over a part of it. If it grows faster than the fish can consume, you don't have to feed them anything else. Duckweed feeds mostly on ammonia though, so it might take up most of the nutrients that you want to grow your plants on. Azolla however can actually fixate nitrogen from the air (with symbiotic bacteria; like legumes). But they might be illegal where you live!



Anyway, back on topic, has anyone experimented with the effect different growbed media have on water or root temperature?
For instance, gravel is probably great as a thermal mass. Also, in a flood and drain setup, does the high surface area of hydroton make for fast heat exchange (air temperature warming it up or cooling it down quickly), or does the high air content of the clay balls actually prevent that, keeping its temperature between cycles? And what is the effect of evaporation (and the cooling effect it creates)?

In warm climates, a media that stays cool during the day and relatively warm during the night would probably be preferable (high thermal mass). But in temperate climates, it might be better (for the plants) to choose a media that warms up more during the day? Any thoughts?