Backyard Aquaponics
A place to discuss aquaponics

I have a relatively new system. I had gold fish in the tank for a couple of weeks and last week my order of 25 Silver Perch fingerling arrived. First couple of days were really hot and the fish were fine. Then we've had some colder days and the water temperature has dropped to 20. I'm finding 2 to 3 dead fish each day.

I bought a test kit from the aquarium shop:

Nitrite: < 0.3 mg/l (lowest reading on the paper)
Ammonia: 0
GH hardness: 10
KH Carbonate hardness: 3
PH: 7.2
CO2: 5 (chart reading)

I don't know how to measure Nitrate, is that another test kit?

Water is crystal clear.

I'm using a 200 L steel drum which was supposed to be ex-food grade however I can see that it is starting to rust on the inside. Could that be harming the fish? I read a post in here that said that the rust was a good thing for the plants.

Theory No 1:
The fingerings which came from livefish may be used to a higher temperature and they're just not used to Adelaide weather.

Theory No 2:
The steel drum with the rust is causing something which is not being picked up in the water tests.

I've put a heater in the drum (which is outside and will cost a fortune in electricity) but I'm not sure that it will have enough affect.

Any thoughts or suggestions?

How are you oxygenating the system?

There are 3 grow beds on flood and drain cycles. When the water dumps back into the drum, there's a lot of bubbles.

I can go out and buy an air pump if that would help.

Just checking...

How big were the fish...

Im assuming when you say Steel, you mean 304 stainless? Unless its 304 stainless.... it isnt food grade.

Iron is an essential trace element for plants.. but "rust" is not in a soluble form that plants can up....

Can't be stainless... if it's rusting...

The fish are very small, about 4 cm

Don't know how big your growbeds are... but even assuming enough filtration....

a 200L drum is just too small to grow out 25 Silver Perch.... look around for an IBC...

Where are you getting your water from? I live in Bendigo and the water from the tap which is supposed to be fine to drink, killed 2 goldfish about 18cm long. IN an hour or so. At a mix of maybe 100L in 500L.

You are in Adelaide where you can;t drink the tap water. What have you been giving the fish?

Dissolved Oxygen (DO) is always good. But if you are turning over your water at reasonable rate and getting lots of bubbles back into the FT, it is unlikely to be an issue. You could add a venturi into the return to the FT.

What is your Ammonia kit like? I am puzzled because at 2 weeks in you should be seeing NH3 in the system. It would seem too early in the cycle to be seeing such low results.

The drum was one from here:
http://www.paramountbrowns.com.au/hardw ... 44-gallon/

They say it's ex-food grade but I guess it's not stainless as it's rusting.

Agree. Ive got my fingers crossed its a red oxide build up on the surface of the stainless. Had to ask




Edit.... stainless doesnt rust as such but it can get a build up of red oxide. Relatively harmless. Try stick a magnet to your drum.... if it sticks, its steel.... and your in trouble.

Thought that might be the case...

IMO... it's a bit late to stock Silver Perch... unless they're at least 100mm (10cm)... even then they'd probably struggle through winter... (and certainly wouldn't grow virtually at all...

Your temperature fluctuations through the day/night... are probably just too much for such small fish to cope with...

Hi Rupert,

The 25 perch are just tiny babies at the moment. They will not be in the drum when they're full sized. Some will go into a second AP set up that I'm planning and others will go to my Dad's system. I thought they'd be fine while they're small but yes, long term it wouldn't work.

Dreaming of an IBC one day

And having introduced another 25 fish.. even though small... I'd be expecting to see some ammonia as well...