Backyard Aquaponics
A place to discuss aquaponics

MAX fish stocking per minimum grow bed/fish tank volumes
3 kg of fish per 100 liters of flood and drain media filled grow beds with 50-100 liters of fish tank
(1 lb of fish per 5 gallons of flood and drain media filled grow beds with 2.5-5 gallons of fish tank)

Ratios
When we talk about ratios it is grow bed to fish tank. A 2:1 ratio means there is twice as much grow bed volume as fish tank. Yes, if you have twice as much grow bed as you have fish tank, you then need a sump tank or some other means to keep from running the fish tank dry.

Pumping
Pump the volume of your fish tank each hour (if pump is running on a timer, pump should move the volume of the fish tank in whatever fraction of an hour it is turned on.)

Aeration
Though flood and drain grow beds provide all the aeration that the plants and bacteria needs, it is good to have supplemental aeration for the fish tanks even if it is not strictly needed to keep the dissolved oxygen up for the fish, the extra circulation provided by the aeration can help keep fish tanks cleaner. Also having a supplemental air pump can make it easy to hook it up for battery backup in case of power failure.
-1 cfm (cubic foot per minute) at 2 psi (pounds per square inch) for 400 gallons of fish tank.-
?aprox 18 liters per minute at 13 kPa for 1000 liters of fish tank

Grow bed Depth
A relatively standard depth for grow beds is 30 cm or 12 inches. This seems to be a good minimum depth that provides plenty of dark space for bacteria, solids filtration, and root depth while still allowing for dry media on top and when using siphons, constantly flooded media at the bottom. It is possible to use shallower beds but they have greater challenges. Deeper beds are definitely functional though they provide less planting surface for the same amount of gravel. Deep beds are a good choice for those wishing to place DWC or NFT growing space after the deep grow beds.

Solids removal
Highly debated topic
If plenty of flood and drain media beds are used, solids removal is not needed.
However, if trying to grow lots of fish with minimal filtration, then the added complexity and labor of solids removal becomes necessary.

TC , The ratio of fish to grow bed volume,
Is this at full grown fish size not fingerlings, no-one ever says

Yep. You base it on the expected max weight of your fish.

Rules of thumb:
If plants look deficient, check pH, add seasol.

If fish "flashing" add 3ppt salt.

What rate os seasol and how frequently can it be added?

Small amounts ofter are always best. I'd go for something like a cap full a week in a 1000L tank with 500L of media. If plants look good, stop..

Fish to filtration

The 3 kg of fish per 100 liters of grow bed is MAX

So if you were to stock 3 kg worth of fingerlings per 100 liters of grow beds, you are already maxed out and you can't expect any fingerlings to grow and survive!!!!! Now if the system is brand new and not cycled and you put the max in right away, the spikes are gonna be huge and survival of the fish unlikely. This is a primary reason to plan for the grown out size, this way the system can cycle up to the load as the fish grow.

So, Stock the system according to the planed grow out size. So if you had a system with only 100 liters of grow bed and have fish you intend to grow out to 1 kg each, then only put in three fish, even if they are tiny at the time you put them in. If you overstock in anticipation of fish deaths, you are guaranteeing yourself some fish deaths. Now just because it is common for one or two out of 100 to die, that doesn't mean that it will happen. Unless of course you overstock in anticipation of deaths, in which case it is quite possible that the overstocking could end you up with no fish surviving a bad spike. It is always best to start slow, this gives your system time to work up to the heavy stocking along with the fish as they grow.

so if i have a 100lt of GB can I get 3 fish that way 1kg each to sustain plant growth? It doesnt seem like it would be enough?

Hi Grombo

You can go higher of course but if something goes wrong (pump dies etc) 100 fish packed into a tank are going to die quicker than 10.

I think I have currently got around 60 kg of fish with only 1,500 litres of filtration so I am well over the mark. Not a big issue as long as everything keeps working but I need to eat some fish soon

On the plant growth side of things you really don't need that many fish at all particularly if you are using good quality fish food that has plenty of nuitrient in it.

Yikes!!!!! If you only have 100 lt of GB and you put 3, 1kg fish into the tank, well I hope the system is already well cycled since big fish often don't like handling and spikes.

The 3 kg of fish per 100 liters of grow bed is the MAX!!!!! MAX amount of fish you should really expect the system to handle if it is well cycled and carefully maintained.

Yes, I know some people might manage to push the limits with a mature system and ample knowledge/experience at taking care of fish but when starting a new system, don't listen to them because with a new system, things always can go wrong and during at least the first season, a system can never support max fish since it is still cycling up and not mature yet.

It doesn't take much fish to support plants in a flood and drain system that doesn't remove solids. It just takes time for the system to mature and build up a nutrient reserve. If you fishless cycle, before adding fish to the system, you will likely have more than enough nutrients to support the plants even if you put in a very minimal amount of fish so long as you feed them good quality feed.

I have had systems keep chugging along with plants for months without fish even without dosing it with anything like humonia. Once the system is up and cycled and has a good ecosystem of worms/fish waste/whatever debris that winds up in the grow beds, they don't need a constant heavy load of fish.

Sorry I don't know what the "minimum" amount of fish is to keep the plants happy, I've never found that there really is a minimum. (See Pee Ponics) I suppose if you find that you run out of nitrates and the plant's lower leaves start yellowing, then you might need some more fish, then again, I've really only seen my nitrate levels drop during winter when my warm water fish were not wanting to eat in the cold water but I still had lots of cool season crops hungrily growing in the grow beds.

Im asking alot of questions as I am very new to AP and I want to learn it all.
I think im going to buy a small heater to promote more feeding activity for the fish.
the only thing thats frustrating is I have had it running for 2 approx 2 months and i havent eaten anything off it.

does anyone know an organic recipe for pest spray as i am getting tinny little caterpillers. they are eating machines

You can find garlic spray recipes on the net, or garlic and chilli etc

I have used dipel in the past for caterpillars... it is a natural bacteria that kills them I think... Safe for fish... none of them died... and I think many members would say so as well...

I think we need to look at lowering the figures being bandied around, to be a RECOMMENDED level of stocking rather than a MAX. I know that these figures have sort of caught on, but I feel that before things go too much further and too many people just assume the MAX is a recommended level it would be wise change it asap... It seems fairly evident that people are often assuming that the figures of 3kg/100L are the norm rather than max.

With our system here at the shop we RECOMMEND people stock 20-25 fish per growbed. Growbeds have 500L of media in them, and that's assuming people will grow the fish up to 500g each. This works out to be about 2kg/100L of growbed media.

In fact I've been recommending people only start with 20 fish per bed, and push it to 25 as a maximum.

I think these figures are more of a safe recommendation level rather than talking about larger maximum stocking levels all the time because you keep having to throw in the "But that is a maximum, you should probably go for less".

Anyone have thoughts on this??

+1 Ivan....But I have learnt the hard way...for great results of dipple you probably should spray weekly..at the least fortnightly and at night.

When I have been bug invaded...and it happens often up here..the plants are as good as stuffed.

Caterpillars are beastly creatures. Those really small ones that can wipe out a patch in no time . They can be squished on the plant as a deterent, to other moths or some species leave behind a web and are found in there, and squished.

You could always make up a batch of chilli pray...that would cook them from the out side in or the inside out