Backyard Aquaponics
A place to discuss aquaponics

The aquarium heaters I have seen all have a minimum setting of around 20C.

Jimmy, the system will take a long time to cycle fully at the cold temps we are having at the moment. Maybe the best bet is to get a few goldfish and leave them and the catfish in the tank for a couple of months until everything cycles fully.


Also ammonia is more toxic at cold temperatures (for the same pH), so this may be part of the problem as well. Have a read of the Ammonia and Nitrate threads in the "Useful Information" section of the forum. Also the link in the top of the quote regarding cycling and temperature has the rest of that info.

Nova

Oops, I see you already have this sorted Jimmy. I read this thread before the other one.

Cheers,
Nova

I think its the other way around nova

I would have to agree with Steve. As pH and temperature decreases more total ammonia can be tolerated.

Ah yes, I read the chart backwards.



I saw the higher level as more toxic, and not as meaning that more ammonia can be tolerated.

Nova

It is the unionised ammonia that is most dangerous and the relative % of total ammonia (ionised and unionised) gets higher as the temp and ph rises.

Okay. With our snazzy digital min/max indoor/outdoor thermometer, it looks like the minimum ambient air temperature was 7 deg C last night (mild, compared to recent nights of 0 to 1), and the water temperature dropped to about 8.9 deg C. By dusk, the maximum water temp had gone up to about 10.6 degrees, whereas the maximum air temp was about 17 degrees. So for a 10-degree air temp fluctuation, we got about a 2.7 degree water temp fluctuation. Time will tell how the water temp responds to a really frosty night.

Any way, we've put a 300-watt aquarium heater in the tank now. It's set to 20 degrees (the minimum temperature) so it'll be on constantly when the timer switch allows it (only at night). In a 1500-litre tank, by my calculations 300W heating power is roughly sufficient to combat about 3 degrees temperature drop over 12 hours. So, this should roughly prevent the water temp dropping when the outside air temp drops by 10 degrees.

We've also bought a bag of insulation batts and Dad will put these around the tank in a few days' time. With any luck this, combined with the heater, might mean we can keep the water temperature above 10 degrees even on the coldest nights. Hopefully this also keeps the bacteria alive and breeding, albeit at a slow rate.

Heating during the evening will probably allow the temp to get higher during the day (ambient) that and, the sunlight getting longr from here on in you should be able to reduce the power consumption if the thermostat is any good.

Yes, but unfortunately the thermostat only goes down to 20 degrees, so whenever the water temp is below 20 the heater will be on full and drawing 300 watts. When the nights are a little warmer and shorter, we'll probably adjust the timer switch to have the heater cut in and out (one hour on, one hour off etc) so as to reduce power consumption. By mid-late spring we can probably get away with turning the heater off until next winter.

Yeh bugger I think I read that before about 20c min, ah well good toiling!

Jimmy, I can't recall if you have a lid on the tank, but that would help keep the heat in, too. Even a tarp thrown over the top would do a lot of good. Trap the warm moist air over the water.

Well, after the first night with the heater on, the water temp was a bit over 10 degrees this morning. Minimum air temp had dropped to 6 degrees overnight.

Will keep you posted, especially once insulation is installed.

At present the fish count appears to be 1 happy silver perch and at most 2 catfish. Can't see the catfish so we're hoping they are both alive and hiding in the rocks...

What sort of catfish did you get Jimmy?

Nova

I believe they are Tandanus tandanus (eel tailed catfish). Basically looks like a tadpole with whiskers.

Just got word from Dad - at dusk last night, the air temp was 10C, and water temp 12C. Obviously because the water was starting the day warmer than before, it was able to finish the day a bit warmer as well. I wonder how warm it was at dawn...

He's reduced the growbed flushing to twice overnight - once at 10pm and once at 2am. During the day I think it flushes every 45min (15-on, 30-off).

As soon as we can:
1. keep the water above 10C
2. observe ammonia levels coming down
3. observe nitrite levels going up then down, and
4. observe nitrates going up,

then we should be ready to try some more fish...