Backyard Aquaponics
A place to discuss aquaponics

How many litres of growbed do you have all up? Sounds like it may be fairly light stocking perhaps..

Hey earthbound,

is a ratio of 1:1.
12t gravel is nearly 10m³ growbed.
And 250 small, and two big is like 300 small fish.
Each should be at harvest time 1kg so i've 300kg, so the ratio is 3kg/100L.

Did i make a calculation error ?

No, the important thing, as you are doing, is to start small and let the system (i.e. bacteria population) grow with your fish.

If you had a new (i.e. something that hasn't matured over 12 months at least) then immmediatly stocking it at the max ratio would overwhelm the bacteria, resulting in ammonia and nitrite buildup, killing your fish.

Hi chillidude,
i've the different part.
I'm feeding as much as fish can eat, but plants needs more.
So i need the amount of fish weight at beginning per 1000L substrate.

Do you understand what my prob is?
I've never a matured system, cause i have to stop system at fall, and start in spring again.
So i need to know how big the fish has to be, to suffer the amount of food.


Dom

maybe at the start, you divide your growbeds up into 3 or 5 sections, start with 1 section when the fish are small, and add sections as they mature and need more food

Hmm ok, but at end i've the same problem like now...
All sections are stocked and fish cannot eat as much as plants want to have...

Does anyone out there know the minimum target for DO for carp? How does it compare to tilapia?

Found it. For carp it is 2mg/L vs 5mg/L for tilapia. Considering that systems running tilapia have been successful at densities of around 70kg/m3 Dom could easily add more fish. The problem is that the system is not being run continuously. In Australia where carp are a noxious fish Dom could regularly add stock until he started to get the nitrate readings that he wanted or reached a stocking capacity of 35kg/m3 (50% due to half size gb) or a little bit over. Once the total mass of fish started to get too big for the gb filter you could either reduce the feed rate or pull out some fish. If the tank was stocked with a mix of large and small fish then maybe they could be harvested but here in Oz they would most likely be fed to the cat or compost heap. Depending on what he is feeding them this may be a bit of a waste or a lot but if Dom is wanting to maximise plant growth by maintaining a matching fish mass/feed rate without having the system stocked all year its going to be a head ache.

In backyard systems rather than trying to maximise the output it is far easier to add more gbs and fts.

Hey thanks for your reply.
Carp are good to eat, we wanna eat them.
Think you're talking about another carp....

I think about adding more fish and remove some fish, or add more Plants with pipes or rafts...
Do you know how much kg fish do you would add at march/april ?
Actually i add 300 fish with 10g => 3kg fish on 10.000L so not very much.
But water was cold (12°C) and feeding rates were low...
So 1% of the fish weight is 30g of food....


Dom

No its the same fish. In australia they are feral and most people wouldn't think of stocking them in tanks or dams even if it wasn't illegal. Here they are noted for a must flavour but they are starting to appear in the fish mongers to serve the asian market. Also there is the human tenancy not to value what is in abundance. In the UK in the 14th century some apprenticeship contacts stipulated that masters could not serve salmon more than three times per week.

If you have done your reading then you will know that a systems capabilities are determined by the feeding rate versus the capacity of the gb to deal with the solid wastes and the size of the ft versus the circulation and aeration rates to provide oxygen to the fish, bacteria and invertebrates. Tom Sp and the UVI system guys ran tilapia at densities of 65-75kg/m3 but Tom had a 2:1 gb:ft ratio amd the UVI systems remove their solids.You only have a one to one ratio so that could limit you to around 35kg/m3. But whileTom sp ran their system without supplememtary aeration and more importantly without a monitoring system he was doing it full time.

If you want to push it add more fish but just a few at a time. However a few in a 10kL a few may be as many as 35kg (10%), even 15kg(5%) would be 5 times what you have now.

If the plants are looking like they need more nutrients, what exactly are the symptoms? What specific deficiencies are you seeing? How good is your fish food? If it's not top quality, it could be deficient in nutrients. Some fish foods are meant to only be supplemental to a fish's diet in another setting, like a pond.

At this stage I think it is most likely that there just aren't enough fish. 3kg with a 10m3 gb is the same is one gold fish per blue barrel gb.

Hi and thanks for your replies.
My water is less on nitrate, and so i decided that all nutrience aren't available enough.
The amount of 3kg was the stocking at spring, or is the 3kg/100L the stocking rate at beginning of the season?
I learned that is the fish weight at the end (harvesting time).

My plants doesn't show any defencies, ecept slow growth...
The question once again, what would you stock (fish weight) per m³ at beginning of an aquaponic session?


Dom

This is not a question that I find easy to answer because I wouldn't have a system that wasn't capable of at least ticking over all year round. Why can't you run your system all year round? There are 4 season systems in Canada and I wouldn't imagine that anywhere in Germany would be colder than Canada except maybe the mountains.

If you want to harvest all the fish at the end of your season you need to work out how fast they will grow and from that work out your smallest size to stock with.

How many to initially stock with is going to be dependent on your skill at juggling all the variables and on the variables that are particular to your system/location. The problem is you probably need to stock advanced fish but you won't be able to stock them all at once. When you first stock with a sizable mass of fish you have to manage the water quality while the system cycles so that the initial amonia and nitrite spike don't kill your fish. You can do this by water changes
and reducing feeding rates and will take around 6 weeks depending on your water temp. Once the system has started to cycle if your really game you can start adding more fish but you'd be better off waiting until the first cycle has finished.

Anyway to answer your question add some fish a few kgs at a time a day or more apart until you get a readable amonium reading in your water. Once the system has finished cycling add some more again until you get an amonium reading and then don't add any more until the system cycles again. You can keep doing this until you get to the level of nitrates that you specified in your first post.

Once you have done this once you will be able to do it better/faster the next time. Then at some point you will get over confident and do it too fast and have a fish kill.

Hey many thanks for your help.
I don't know the temperatur in canada, but last year we'd -21°C in the winter.
So i think the bacteria and plants will die in this time.
The carp stay in the pond, thats not the problem, and i can start with bigger ones, but then its possible that i can't feed them much at beginning.

I think the balance isn't easy as i thought...
The tomatoes have a little defency, the new leaves are small and purple.
Seems like phosphorus, but my food contains 1% phosphorus...


Dom