Backyard Aquaponics
A place to discuss aquaponics

Guys

I'm just trying clarify this concept of a 2:1 grow bed to tank volume ratio.

A few examples to explain,

if I run a 200 litre bath tub then logically I can run 400 litres of growbed. Thats 2 blue barrels worth, 4 half barrels. You can fit a lot of plants into 4 half barrels yet I can't see fish getting too large in such a small space. Therefore my concern is insufficient amonium to produce adequate nitrates.

Next, a 1,500 litre system could support 3,000 litres of grow beds or 30 half barrels. Again, thats a masive nutrient draw down to support plant growth.

When I see new systems that seem to support rapid plant growth with seemingly small fingerling numbers I ask myself what I am doing wrong. Joels commercial systems come to mind, and others.

Please feel free to comment and help clarify this.

thanks
Derek

Hi Derek - am I to assume from this post that you are having trouble keeping up the nitrate levels? Not a problem that I ever had - even when I just had fingerlings. Give us some details that might help further in idetnifying your issue. What fish and how many do you have. How much are you feeding. What do you have in the way of GBs and what is growing in them. What is your nitrate level atm.

Hi VB, Yes my system and I have issues but I didn't start this thread to analyse my system. I have never seen any definitive comments regarding the ratio. I would think more water than gravel was better. Maybe my nitrates are too diluted.

There has been endless discussion about the ratios Derek and the fact that they are not meant to be definitive. The 2:1 is a guide only and is used to help determine the stocking density that could be safely kept (max 6kg per 100 litres). Full regard needs to be had to many other factors such as feeding rate and planting rate also.

If you are registerring nitrates then that would tend to indicate that you have surplus to the plants needs - otherwise they would strip them all out.

If you need some help with your system - post your probs in your thread and we will see if there is anything that we can help with.

does having a powerful pump help?

That is if you done have a flood and drain system?

Then the water would get circled around much more

Does it help?

I agree VB, there has been endless references to the ratio. This thread isn't going the way I anticipated it might so I'm happy to drop or delete this thread.

cheers

No that's cool Derek - just clarify for me what it is that you want people to comment on. If need be - I can delete the middle posts.

derekh-
We also say to assume can make an ass out of u & me.
So I say, seems you have a handle on the concept, 2:1 ratio.
What is it that you're unsure about?
Fish?
Plant load?
I am sure we can work it out!

Hi Derek,
There are other factors in supporting rapid plant growth. My big problem is lack of sunlight. So while I have problems growing some crop plants, my tropicals (elephant ear, caladium, begonia, peace lily, tree fern, etc) are doing incredibly well. Another factor is how much food you actually give the fish. For my tilapia and the size they are, I should be feeding about 3% of their body weight. I'm feeding less because I have a surplus of nitrate and am trying to get that back down. The 2:1 ratio is what a lot of us strive for, but I have heard of systems with 5:1 or even 8:1. It depends on what you want to emphasize and what you have the space for.

CC, having a -sufficient- pump is important. Too powerful and we blow the fish out of the water. My pump is sufficient to turn over the water 3x/hour plus circulate the tank. I did have a smaller pump, but didn't feel I was getting enough out of the nitrogen cycle. I think I turn over the water more frequently than most people here, but I'm not sure.

Yep Janet, 3 times/hour is a good turnover rate to work at, unfortunately as the tanks get bigger this is hard to achieve (and not blow the fish out of the water), worked mine out to be around once every 2 hours through the GBs and the same with a tap aerating straight back into the sump tank.

Wonder if this could be the cause of my nitrite levels staying at 0.5...must do some checking (modifying )

I aim to keep it at once every hour with my relatively low stocking rate. With the way I have setup my system - if I want to increase the rate (which I will do as I add more GBs) I will just add another pump to the sump.

Yeah, I can't get the water to turnover at more than once every two hours either, not without doubling the pump size

It takes about 40 minutes to fill the two big grow beds, the blue drums fill and drain a couple of times during that period.

or halving the tank size

Tisk tisk!