Backyard Aquaponics
A place to discuss aquaponics

I have read that the optimum for fish stocking is to use twice the fish tank volume in growbeds.

But it seems to me this is not very practical or common. Are there some good examples of systems that have this ratio? My current system is chift pist 1100L tank, 500L sump, filling to 700L (about 350L water) on my GB drains my sump to shallow levels. Therefore I have about 43% GB volume to the water in the system.

It seems to me that I need serial filling GB's to achieve this 2:1 ratio but I am only aware of Les's (EllKayBee's) system that is serial. Am I missing something? Or is this ratio not usually achieved?

Novaris - Its more about stocking densities!
At a given (heavy) ratio of fish load to GB 2:1 is required.
Since most of us have a lighter fish load so is the ratio.

So does it matter much how dense the stocking level is? I mean is there a minimum guideline as to the amount of fish to plants or fish to GB volume?

For example if I had 1kg fish in 1k L tank and 2k L GB's would I get enough nutrients for the plants? Or would the nutrient density be too low? Would it be better to have 1K L of GB?

It is more important to me to produce fish than vegetables so my aim is to have 3 GB's in series that can be added in as the weight of fish increases. But I am wondering if once they are running if my stock levels drop i.e if I have to cull the trout in summer should I remove some beds or just leave them all running?

There is plenty of conjecture on this subject...
max is 6kg/100ltrs
that is like a sardine can before opening!

I had seen this my plan is to try for 4Kg/100L of tank which is 2.5Kg/100L of actual water in the system.

I just read the 2 to 1 growbed topic, thanks.

still, I am left with the feeling that 2:1 generally is not used and stock level generally don't approach 6kg/100L.

Is it likely that I can achieve my target stock level with three 700-800L GB's would 2 be enough?

Currently my nitrates are at about 40 with 50 odd trout maybe 4.5 Kg of fish and my plants which are from seed are just starting to grow now. Cold weather has meant that the main bed has not yet fully cycled but ammonia is sitting at 0.5 and nitrite at 0.25 thanks to the 200L temporary GB I started with.

4444

Without knowing your system stats... I should go and read up but too lazy
I don't want to give you false hope...
(Quote - I had seen this my plan is to try for 4Kg/100L of tank which is 2.5Kg/100L of actual water in the system.)

What do you mean actual water??
How much water is in your system?

After asking an annoying number of questions on this topic I should probably answer a few.

The 2:1 ratio is more of a guideline rather than a rule. The more fish you have the more plant area and plants you will need to use up the nutrients. However different plants use nutrients at different rates so if you are growing nutrient hungry plants you won't need as much planting space.

I reckon it is practically impossible to design a system that factors in all the variables in fish growth and plant production and therefore a system should be designed to be flexible and stable. If you want to focus on the cweeture side of things then maybe consider doing water changes, having dedicated fish food growing GBs or stock feed GBs.

One of the problems with running a lot of fish with a smaller biofilter (growbed), the 'solids' tend to overwhelm the filter - it is capable of converting all the ammonia, but cant keep up with 'solids'.

This leads to the bed becoming choked and fish dyeing.

6kg per 100 litres is a lot, but would be close to achievable - except for the 'solids' - take care of that, and you too can have sardines without a tin.

I am running about 1.5:1 Growbed volume to tank volume.
The ratio is for growbed gravel volume compared to actual fish tank volume (sump tank volumes should only be added into the figures if you are raising fish in that water.) You are not figuring the amount of water in the grow beds or the amount of total water in the system. It is more about surface are for bacteria and plant growing compared to fish stocking density but those can be hard to figure. Yes, to get the full 2:1 ratio does require either a very big sump or cascading grow beds and that is probably one of the reasons most people don't have the full 2:1.

I'm not quite as good on the how much fish per amount of water figures but the 2:1 ratio should give enough filtration and nutrient uptake space for a high stocking density. Most people actually run lighter stocking densities.

As to having extra grow beds to add in to take up more nutrients when stocking is high and cutting it out when stocking is low is not how I would do it. Most people will keep all the gravel beds online (flooding/draining) no matter what the stocking but if there aren't enough nutrients, pull out some of the plants. If the nutrient levels are rising, plant more plants. If you were to take the bed offline, the bacteria is going to die and the solids in the bed are going to rot and the worms may dry out and you have a stinky mess hiding in the gravel. Might as well leave it in line and adjust the planting to suit. Aquaponics is all a balancing act.

So system is 1600L of water.



Thanks Stuart, I am thinking I am probably concerned more with area for nitrogen cycle than for plants. Plants can be added or removed easily but bacteria cant reproduce as easily especially in cold weather.



Qutbackozzie this is really starting to help

So in a system that runs 1600L water and 2400L gravel GB's would there enough capacity to easily cope with 4kg/100L (i.e 60-65Kg) fish solids? Also I notice some people run the water in around the GB not just at one entry point, is this to better distribute the solids? Does it make a significant difference?

how much would worms help with the solids?

Navaris - you should be able to have that sort of capacity, but if something goes wrong, its gonna go wrong real bad.

Worms help a lot with 'solids' but too much and they get choked as well.

Multiple points of water entry will help disperse the 'solids' but they will still build up.

A swirl filter pre grow beds could assist ,, drain to dirt garden . But it is getting away from the KISS system that AP is suppose to be.
On the other hand , I know a lot of people enjoy to tinker and see how far they can push the theretical limits:)
By some cats ,, no use wasting dead fish. But what you learn could be valuable information for others on here.

Cheers

I am sticking with the multiple outlet points, I feel build up will process the solids to be handled by the GBs.(so long as the ratio is 2:1 or less)
If you notice the solids build up on the imediate surface, you can always gently rake the 'media' to replace with cleaner 'media' from near by,
if you feel the need.

I disagree (LOL) with the cat thingy because my dog loves whole fresh fish!Dead or alive...
I prefer the Blue wrens and other flora mice!