Backyard Aquaponics
A place to discuss aquaponics

yeah I know all depends on their size but with
1000L F/T, 2 x 400 L sumps, 5 x 300 L (?) gravel grow beds,
1000L/H pump from sump to F/T
gravity to grow beds,
siphons into sumps

what number of hard as nails, survive anything...(well almost anything) plain common goldfish can I aspire to, currently have about 30 varying in size from 6cm - 14cm

I've had goldfish, plain & Shubunkins, to about 12cm, in a number of systems and I worked on 5L-7L of wet gravel per fish, dependent on size, and never had any issues with Amm.

so therefore ...5 grow beds @ approx 300L/400L = 1500L wet gravel divide by your 5L wet gravel = 300 fish holey moley batman that cant be right.

I think there is an ethical side to the question as well...
just because you theoretically can doesn't mean you should...

In my opinion while you can technically stock around 50 goldfish/other fish 200-300g in an IBC of 1000L doesnt mean you should. If it looks cramped it most certainly is....and that becomes the basis for animal cruelty..

For an IBC around 700-900 Litres (what you basically have) I think 10 is low stocking, 15-20 is moderate stocking and 25-30 is probably a nice persons upper limit.....

the BS that some people post about 50 plus is the zone for certified cruel idiots ....
(unless they are fingerlings/juveniles and you have some plan to thin them out over time)

Personally I think it is not nice to have to swim and live 24/7 in a 20L bucket, so that means 30+ is getting cramped..
nice people probably think 30-50L is OK so hence the 20 or so fish...

so easiest way is to look at a 20 litre bucket and think how many fish you would be happy putting in there, presumably less as they get bigger... then simply case of making sure you have enough wet media.

The exception is where you are doing real AP, have a big circular tank (3000-5000L) and are trying to make things work.

incidently - an IBC holding 1000L is pretty much a myth as well.
That is its filled to top transport capacity, once cut in some way more like 900L max (and often less)

good point Darren. thinking like that

Long term you wont need many

You will need enough to keep your nitrates in the orange colour on the "API" Chart in the test kit .

So how long is a piece of string once the fish grow you will need less , if your beds are full of overgrown tomatoes you will need more

It just comes down to how much feed you put in to balance your system .

If your system needs a bit more input a splash of ammonia and seasol is not hard .