Backyard Aquaponics
A place to discuss aquaponics

I am building my first small aquaponics system in a greenhouse in the Netherlands.
I have been reading and watching video's about aquaponics the entire winter, I dug in my fishtank and sump and build the growbeds. The time slowly aproaches to add fish, or at least reserve them at a dealer.
But how many? I have read so many different things that I dont know anymore, ranging from 10 to 60 fish for an IBC system.

My fishtank is 800 litres, sump is 240 litres (pump in sump). Main growbed is 250-275 litres, one growbed of 50 litres, A raft bed 50 litres / 30cm by 60 cm surface, and a 2 meter standpipe for strawberry's. Oh and there are some edible waterplants in/above the fishtank. growbeds wil cycle 5 times an hour, and I have a strong air pump and six large bubble stones to add plenty of air.
I will be adding Grasscarp, they can handle high temperature in the greenhouse in the summer and low temperature in the winter.
The dealer has fish available of 7-10 cm, how many would you put in?

Thanx in advance for the advice!

It all comes down to bio-filtration capacity.

Use a Wet Gravel:Fish ratio of 20L:1 for slow growing fish, 25L:1 for fast growing fish such as Trout.

This ratio will give you a safe fish stocking capacity through to a size of 500gm each. You could stock at a higher rate when they are smaller, so as to make more nutrient available to the plants, but you will need to move some fish out of the system as they grow and your system reaches it's maximum safe capacity.

Yep, what damage says.
But, size of the fish tank is also relevant, all well and good having a biofilter able to process 100 fish but I wouldn't put 100 fish into an ibc and expect them to happily live.
I have 60 fish in a 3000l tank and it looks crowded.
I think 20 fish max in an ibc is the limit but I've seen much more unfortunately. Stagger the sizes and only add a few to begin with.

Hi Giel, welcome to the forum (another Dutchy).

Hoi Giel, welkom op dit forum (een andere Nederlander)

Thanx for the explanation!
So in my case 15, 16 or 17 fish would be ok. (unless they get bigger than 500 grams)
Do I understand correctly that the system will be "safer" or "less volatile" if I put in less fish, for example 12?

Hey Wilsil thanx for the welcome! groeten uit brabant!

To all those points you should also consider how mature your GBs are and how many and what stage the plants are. The more fish the higher the capacity to chew nutes is required.

Change of plans.....(not the first time)
In the end I decided to forget about the edible fish. I bought some (non edible) fish that dont get bigger than 8 cm, so fhe Ibc tank is big enough for them to swim around. so far they seem very happy in there.
I have lost two fish but I think it was because of the transportation. I bought them on a very hot day, drove for one hour and got stuck in a traffic jam, they were dead the next day. The rest has been in there for one week now.
Now I have these fish in my tank:
-5 mona lisa, 8 cm
-10 mona lisa, 5 cm
-32 rainbow shiners 4/5 cm
-17 White Cloud Mountain Minnow 3/4 cm

I think 15 Grasscarp of 10 cm would have eaten and shit more than all of these together.
Do you think I have enough fish to start up the system? Or to many or to little?

I bought a water test kit today so I will post results tomorrow.
For now the fish seem happy and the plants are growing and look healthy.

Thanx in advance for the advice!

The test kit will guide you on how many fish you will need long term

This can change through the seasons which complicates management

Plants such as Big Tomatoes will use up more Nitrate than small seedlings

Keep on top of your Nitrate / Ammonia as high levels mess with plant health and invite unwanted bugs !!!!!!!!

Keep your system in the 5ppm to 20ppm Nitrate range (Orange colour on the API freshwater test kit)

This comes with experience (Lots of testing in the beginning)

Keeping our systems balanced by increase or decrease of fish feed due to season / fish numbers / size / Plant type is a continual learning curve and very rewarding once (if ever) mastered , lots of variables .

Growing quality plants requires quality inputs

What will you be feeding these fish

For example goldfish flakes don't offer much nutrition for big hungry plants

Some ornamental fish don't cope well with high protein aquaculture feed

And WHERE are the photos we love photos

Have fun cheers

Thanx a lot Terra for taking the time to explain, that really helps a lot!
You deserve some photos!!!

I am feeding them with food that "came with the fish". Bought the rainbow shiners at a "specialized dealer" he sold me a small box with mini pellets to feed them. Does not look like the regular gold fish flakes or pellets. Its all brown instead of multicolor and it smells superstrong! I will call the dealer to ask about it. (the box does not have a label)

still not entirely finished but here is my first AP system:


Two flood and drain growbeds, sump and a "raft bed".




The fishtank:
I will be planting watermint and watercress to give the water more shade.
The males have started to chase the girls the last few days because water temp is increasing so I gave them a tray with pebbles in case they want to lay eggs.


some of the fish:







Note: The water lily is only in there to help the start up and for some shade. I had the 5 mona lisa's in a tank with the water lily and some other plants as a little pond. so I figured the clay pellets in the basket would already be colonized by bacteria and help the start up. I will be taking it out in the future when the plants in the growbeds need the nutrients.

Just tested the water.
pH 7.5
KH 5
NO2 0.2
NO3 6
Fe 0


Should I also get a NH4 test?