Backyard Aquaponics
A place to discuss aquaponics

What is the temp of the tank? Did we ever determine whether the tank is lined with anything (ie like aquaplate)?

It's a standard, new, galvanised iron rainwater tank. Zincalume I think.

Haven't tested the water temperature but it is not heated externally and given the fact that it resides inside a shed I'm guessing it doesn't get any warmer than, say, the average ambient temperature (avg of max and min). That'd be somewhere around the 5-10 degree mark of late.

Should we install a secondhand solar pool heater or something, to keep it warm during winter?

I am wondering what they used to seal the joins Jummy. To me, it sounds like contamination of some sort. A temp reading would be good. Mine are showing no signs of stress at 6.5 if that is any indication of what they will tolerate

Jimmy - It is a bit hard to diagnose without all the info. First - get us the tank temp, but I am also inclined to think it may be a contamination issue to do with the tank. I would probably bite the bullet and put any remaining fish into a little tank or something, empty the big tank, clean it thoroughly and then start again. Of course, being an unsealed tank - cleaning it may not fix the contamination problem (if it is that), but it may well. The other option is to paint the inside with a food and fish safe sealer before refilling.

How many fish do you have left. IMHO - buying more fish when you have not resolved your existing issues is not a practical thing to do.

yeah, the problem definately sounds to be an environemntal problem rather than disease

The fact that several fish remain alive is confusing, to say the least. If it's a contaminant then I'd expect it to kill them all. Dad's going to get a temperature reading asap.

If the remaining few fish keel over, we'll have no choice but to drain the system and start again. Certainly won't be buying any more fish for a while...

if you've done a water change any contaminant may have been diluted?

Haven't done a water change as yet. That'll be the next thing.

Have you done a water change at all since they started to die?

I can't recall, but did you ever test for nitrites? Where did the water come from tap/rain/bore?

I think we may be able to rule this all down to temperature and the efficiency of the bio filtration.

Tested temperature at 11am, it was about 7.5 degrees, and is now 9.4 at 2:30pm. Dad will get a reading at dawn tomorrow, but given the fast response over the last few hours I'd expect it to drop down to close to ambient temperature (0-1) by dawn.

pH is 7.8 to 7.9

Ammonia is between 1 and 2 ppm.

Have not yet tested for nitrites (don't have the kit) but the high NH3 suggests that the bacteria are not yet working sufficiently. This is supported by the low temperature.

Current plan:
1. Reduce growbed cycle frequency at night time, to keep the water in one large mass as much as possible. Probably make a single flush around midnight.
2. Invest in an immersion heater, put on a timer switch to turn on just after the midnight flush, and heat the water up to about 10-12 degrees C. This will not draw too much power but will prevent the water dropping to dangerous levels during the coldest part of the night.

Thoughts?

I would also get some bubble wrap or similar insulation to wrap around the tanks. Keeps the heat in.

Jimmy my pump turns of 530 pm and on 830 am with no apparent problems to the plants

or fish

except it will be a bit different if the system isn't cycled. Although, given the problems, I would do a 50% water change and then not cycle for the 14 coldest hours. Also, cover the tank.

Most aquarium heaters have a thermostat that you could just set and leave it instead of using a timer. I'm not sure if they go as low as 12C, though. Maybe check pond supplies?