Backyard Aquaponics
A place to discuss aquaponics

derekh, have you actually measured your nitrate, or is it more of a philosophical question?

If is the latter then my advice is don't over analyse it unless you're prepared to measure all the variables which might be a good idea if your system is not performing to expectations. There can be soooo many things that will stunt plant growth. a high PH for one.

I have seen 20+ plants supported by 10 <10cm silver perch fingerlings.

The grow bed ratio is the max stocking density...

100 ltr of water to 200 ltr growbed ... but you dont HAVE to put 6kg of fish in there...

You could put 1.5 Kgs of fish and still have enough nutrients... what do you think steve...

Roy

for sure.

1.5kgs would give you more than enough nutes (if the fish were feeding) for two bath tubs of plants IMHO

The six goldfish and 6 tan tans that we put in steems fingerling tank when the silvers were moved into their new home have made a significant difference to plant health and growth (they are all feeding wheras the silvers weren't) so IMHO It doesn't take many fish.

Just ask steve and anges courtyard system with a 120 lt aqurium

what about when you've got not much fish is alot of water. I've got 30 10cm silvers in 3500ltr tank with 4 of the 16 bathtubs cycling. Plants are growing much slower than my dirt garden.

Worms, it will mean that the level of nitrate will climb more slowly (its exactly this that adds stability and safety to large water volumes)

The MAIN thing to remember is ultimately its the amount you feed versus the amount the plants take.

when the amounts are balanced then the nitrate will stay at a given figure.

If you fish to plants are balanced but you want to increase the base level of nitrates then you need to either add more fish (or feed more) or remove some plants FOR A WHILE.

Does this make sense?

I'm still in the process of setting up my system and my GB to Tank is 1:2. I'll have to understock my Tank until additional GB's can be build. (Worked all weekend on my system and feel like a beaten dog. Going from a computer job to a labor job is hardwork.)

This thread is of value I most likely would have reduced my tank (pond) size if I had seen this before starting the project.

Is sounds like a balancing act just like my aquarium setups with fish to emerged plant ratios? I add ferts that are fish friendly 3x a week to makeup for what’s not in the fish food so plant grow can be maintained.

Hi Bkausfish,
Understocking isn't all bad. If you have a pump or power failure, the DO won't fall as rapidly.

You are right, it is all a balancing act. Growbed volume, tank volume, #fish, food, plant mass, pH, system maturity, sunlight,.....,there's probably more.

Janet is most certainly correct!

nothing wrong with having twice the water that you need. It adds stability in every way. temp, PH, etc.

You are WAY better off to be understocked than the reverse. Janet, Steve, and many others have mentioned the benefits of large systems in their ability to be more stable. This is ofcourse still assuming their ratios to everything else.

I have 15,000 + gal.s of water and I could fit most of my fish into 2 of Janets systems. She has to watch hers closely, while if my pump goes out, my fish would likely not even know it for a week or so. And if the feeding stopped at the same time as the pump, then they may never know it since they would go to eating what ever was produced by the pond/pool.

Being understcked will allow you much more room for learning, etc. Then you can increase as you become more comfortable.

No sense in getting in TOO much of a hurry.

I have just added a nother 1000 litre to my system new cabbage are a bit slow now cold weather and using fish water for dirt garden [so top ups every 3 weeks] now its a lot more stable Bugger building second system just add to the first

This is what I don't get about the 2:1 thing.

Lets say I have a 6000l grow bed, 30cm deep, and a 3000l tank.
Lets say my stand pipe is 6cm below the top of the gravel.
To fill the grow bed to the stand pipe would take 4800l of water, except that its full of gravel.

Now how much does the gravel displace?
i.e. what volume of water do I have to pump up to flood the gravel bed?

I would guess the gravel would displace 50% of the volume so I'd need 2400l of water. Now I've only got 600l of water in my tank ... poor fishy!

So I either need a bigger tank or some ballast water in a sump or something. Which means my 2:1 is now more like 1:1!!

I think I must be missing something!

2:1 is virtually impossible unless you are running chift pist and have a big sump

Samantha,
To achieve 2:1, you either need a chift pist setup as Monya said, or several growbeds with alternate fill times, or a similar strategy.

1/3 voids in gravel is a good generalisation. So a 6000L growbed would hold 2000L of water.
Generally recommend 2-3cm water level below the gravel surface, assume it goes right to the surface for any volume calcs.

Alternatively you can just run at a lower ratio but stock lower quantities of fish accordingly.