Backyard Aquaponics
A place to discuss aquaponics

Can red worms be added to a new system? I'm afraid there might not be enough food available for them. Also, how many should I add? I have about 9 square feet of surface area. I have a 20 gal tank and two small grow beds (each 1.5 x 3 feet) set up in my kitchen. How many goldfish (the 0.35 cent kind at Pet Smart) should I have?

It's fine to add them to a new system. Just add a few handfuls and they will build up their numbers as the system matures


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Hi ldelo1,

The worms can go into a new system but there will be a limited amount of food for them until your solids build up so don't put in too many. As Bender notes their numbers will build up - but you only have small beds, so only a few will be quite happy.

The goldfish questions depends on a lot of factors, but primarily size - stocking rate is really a case of size(weight) to filtering/grow bed, but in small tank case water volume is most limiting. As the fish get larger less goldlfish will do the job - basically it is a function of feeding and ammonia generation.

My 500-700L (130gal) tanks do fine with 10 or so fish, usually a mix of smaller and larger fish and I would not go more than 15-20. You will have to supplement with Seasol etc anyway.

For 20gal (80L) you should not go overboard, at medium size you will probably only comfortably support 4-5 (around 5gal/fish*) and they probably wont grow large. So initially (presuming small) starting with 6 would be fair. If you have a plan or option to move a few out/on then you could go with a slightly higher number.

There are posts of people putting lots in, and even posts where completely ridiculous numbers are put in.
But it is not really fair on the fish and usually in those threads many die.....

* simply google "how many goldfish 20 gal fish tank" and you will see 2-4 goldfish as a typical aquarium number. With constant filtering AP can support at the higher end but not too many.

Thanks for the info.

I had 7 goldies in my first system, a 75 liter FT with a similar ST and GB. They grew to a very meaty fist size and were very happy in the system and growth was phenomenal, up until it rained one day and the pump shorted out with the FT water, oh God the horror.

Anyhew later I had 6 goldies along with 3 tilapia in a bathtub and they powered the same 75 liter GB just fine, quite well actually, grew sweet melons in that.

So yea it's surprising how few fish you need, but still I feel 10 fish in 700 liters is a bit underpowering the system, especially if you're not counting on growing them out to full plate size. I figure 50 liters per goldie is enough as per Mother Google, ratios for stocking grow out/feeding fish will of course differ.