Backyard Aquaponics
A place to discuss aquaponics

Hi,
As promised in the introduction section here is my planned beginner-system (BS)
A very simple system I believe. At the bottom we have a 1000 l plastic container in which the fish are kept. On top of this is placed 4 x 150 l containers as growbeds. The growbeds are filled with clay balls (if I can source them or make them ..and I am not keen on making them!) or with gravel in the 13mm range.
A pump fills the 4 growbeds to just below the top of the gravel and then switches off for the time it takes for them to drain back into the tank below. Timer then switches the pump on again for the next flood and drain cycle.
The growbeds will be used for whatever vegetables work and a bit of herbs. The fish would be for the aqaurium hobby and either livebearers or some v egetarian/algae eaters. I may add floats if I find the plants are not pulling enough nitrates out of the water.
I have attached two sketches to give an idea of how this wil look.


Ok Now my questions:
I will be removing say about 500 l on every flood, after having removed the top of the 1000 l I should have about 400 left in there on every flood, is this enough for the fish given that they will be small (5-10cm) and what negatives can I expect from this?
In the growbeds I would like to put in overflow drains so that if something goes wrong the beds dont get too much water. Am I correct in saying that these should be a large diamter pipe and my "normal" drain should be a much smaller diametre.
Am I correct in saying the flood should be fast and the drain slow?
Does the next flood start as soon as the draining is complete or is there a break inbetween?
Ok thats enough questions for now!
Please feel free to comment and add things that I have not asked about in my ignorance!
Cheers,
KarelM

As long as you stock at the correct density for 400l of water thats fine.

Actually, 4 x 150l growbeds will only hold around 250 liters of water, so that helps a bit.

Overflows and normal drains can be the same size, a V-cut into the side of the growbeds will work fine as an overflow, considering the beds are over the top of the tank. 19mm pipe will be more than sufficient for your drains.

Flood fast, drain slow - drain fast, flood slow - there is not really much of a difference. The preferred method is to flood slow, and drain fast - drawing more air into the root zone. I have not seen any difference in growth either way.

The next cycle can start straight away, or be left for hours. Depends on your climate, stocking density, and water quality. More cycles = better water.

Thanks Ozzie,
Something else that is confusing me is where is the actual de-nitrification tacking place?
Having kept fish for jonks I know the cycle but have always been taught that you need a bio media that stays wet for the various bacteria to attach to. Which is what I do not see in any of the systems here.
If it is on the media in the GB then that media should be porous to give enough growth surface and yet peopl have loads of success with plain gravel.. Also the media should be kept wet all the time, yet people switch off their systems at night??
Thanks again,
KarelM

You're correct Karel... the nitrification process takes place in the growbeds...

To be specific... in the water that surrounds/clings to the media ... even media like gravel maintains a layer of water around it for up to several days (depending on temps)....

If you dig into your media... even at the end of the drain cycle... it's still moist...

Some media... like expanded clay is semi-porus... having microscopic holes all over the surface... but utlimately it's the layer of water held around the media by surface tension... that houses the bacteria...

Some more porus media... just holds the moist layer for longer... but in normal circumstances... it's just not an issue...

You can get Hydroton in Cape Town in Ob's - just don't know the price

http://www.windell.co.za/prod_media_a01.htm

Yep, the bio-filter is the media filled flood and drain grow bed and the plants take care of the nitrate instead of needing to do water changes all the time. The media below the surface stays plenty wet enough for a period of time to do the job.
A grow bed when filled with gravel will only hold 40-50% of it's volume in water so even if you had 1000 l worth of grow bed, you would still have at least 500 l left in a 1000 l fish tank during a flood cycle.

You might think carefully about placing the grow beds directly over the fish tank, It might make accessing things tricky but that is just my interpretation.

Anyway, welcome to the maddness, there is no cure, enjoy!

OB1 thanks for the heads up on the grow shop in South Africa...they seem to have some nice goodies!
The placing of the growbeds on my bad drawings are not really correct, I am hoping to have them very much on the edge of the fishtank.
k so when people talk about a 1:1 ratio or 1:2 etc are they talking volume or volume of water.... so if I want a 1:1 ratio I will need a 1liter tank and a 1liter GB or a 1L tank and a 2L GB that after media has space for 1 L of water?
And should I waite until the tank ahs completely cycled (ie showing 0 amonia) before planting as it is only then that nitrate is availible or can one begin planting as soon as the fish go in?
Cheers,
KarelM

When people talk 1:1 ratio... or 2:1 ratio... it's growbed (filtration) volume : tank volume...

Ideally, as a minimum you need at least as much filtration volume as your fish tank volume... for simplicity growbed volume:tank volume...

It differs slightly, is as much as the actual volume of the growbed is greater than the actual media filtration volume... typically the media will take up about 60% of the growbed volume...

Hence it's often suggested... particularly for higher stocking densities to aim for a 2:1 ratio... which also allows for more plants...

Other factors, such as flow rate, influence the filtration requirement... you should aim to turnover (for aeration) your tank volume at least once/hour...

There's no real reason why you can't plant out your growbeds immediately... indeed that's what is advised with all the BYAP System kits...

If need be, you can boost the plants, in the initial absence of nitrates, while you cycle with the addition of Seasol or Maxicrop... liquid seaweed extracts...

..ok sorry rupert you have confused me more.
Do I take the volume of my grow bed as an empty container or as a container filled with media; so please choose your weapons:
Option A: my fish are in 100 L ; I have a 100 L GB filled with media so I can put 50 L of water in there. This is a 1:1 system.
Option B: my fish are in a 100 L; I have a 200 L GB filled with media so I can put a 100 L of water in there. This is a 1:1 system.
Option C: Karel has had to many beers tonight and should wait until the mornign and then expriment with some sand and breakfast bowls in the kitchen.
OK, what is it?
THANKS,
KarelM

Relax, don't eat the sand for breakfast with a hangover though.

Just judge the numbers bassed on your container volumes.
If ya got a 100 l bin for a grow bed and a 100 l bin for a fish tank then your system is 1:1
If you have 2, 100 l bins for grow beds and only one 100 l bin for fish tank then your system is 2:1

The amount of water that can fit in a 100 l bin already filled with gravel doesn't have anything to do with the growbed to fish tank ratio, it is simply handy to know that the gravel often takes up about 60% of the space so you only need about 40% of the water in order to flood a gravel filled grow bed. These numbers are of course aprox since gravels vary. Sand will probably give a rather different view of this whole discussion as it packs in tighter.

Now a 1:1 system can be pretty simple as even when the 100 l grow bed is flooded there will probably still be about 60 l of water left in the fish tank, this can be ok if not too heavily stocked.

However a 2:1 system would not have much water left in the fish tank if all it had was a tank and the grow beds and flooded the beds all at once. To deal with this people either have a sump tank to absorb level fluctuations, multiple pumps to flood beds alternately, try to cascade beds or other ideas out there.

Good luck

Concise as usual TCL

Soory if I confused you Karel... go with TCLs explaination for simplicity...

Ok,
Thanks all...I have got it!
I am not to concerned with having too little water left in the tank as I am going to work with small ornamentals that should have a low biomass. My concern is now turning towards whether they are going to give enough amonia to result in suffiecient nitrates for the plants.
Hmmm the other thing that I see hapening is that as they grow (and multiply) they are going to produce more amonia for which a person needs more plants....I am going to love this balancing act!!!
Thanks once again for all the inputs and help.
As soon as I start setting this up I'll post some pics!
Cheers,
KarelM