Backyard Aquaponics
A place to discuss aquaponics

We had a pretty big drop in temp last night due to the southerly that just blew up the East Coast of Aus. They system http://www.backyardaquaponics.com/forum/viewtopic.php?f=18&t=21334 is really well insulated so I was shocked to find a 4 C drop overnight. But I do remember the guy at the fish farm mentioned that if the pump was blowing cold air into the tank it would cool down the water and the insulation as exacerbated the problem by not allowing it to heat through the day.

So to the question if I was to make a large cover with a lot of airspace for the pump and attached something like a hair dryer with a thermostat switch to keep the air temp around the 50 c mark say, would this be a reasonable heater to win back a few degrees to keep the Silver Perch growing over winter?

Feeling it up here in the North too mate, crap it got cold last night. Blowing a gail here today, feels like its straight off the arctic.

I imagine it would be cheaper to switch off the air and run an aquarium heater. Fighting a loosing battle though most likely.

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Whoops, I missed the question. No, that would be a waste of time. Your SP will be fine through winter but feed will be at a minimal. Forget about pellets try things like cheap prawn tails, yabbie, snails, worms etc. Grow leafy greens.

SP are a summer fish and will lay dormant in the cooler months.

hahah if this weather keeps up probably should try my hand at trout :p. Was really hoping to extend there growing season. It was strange the water was up around 19 - 20 they were feeding really heavily. Then a few days before the cold weather they started getting real lazy and not feeding even though the water was still warm... And when I was talking to my grandmother it seemed that corresponded with a barometer drop. Anyone else notice this type of behaviour before?

Yes, fish often go off the feed on a rapidly falling barometer (in rivers too, if you are trying to catch them), and it did start falling a couple of days before the change, and they start eating again as it rises after a front has passed.

[quote="nwillis"]. But I do remember the guy at the fish farm mentioned that if the pump was blowing cold air into the tank it would cool down the water and the insulation as exacerbated the problem by not allowing it to heat through the day.

My air pump lives inside an old fridge (idea by CC Bear). It stays pretty warm in there due to the heat created by the pump itself. I've insulated the air delivery hoses right up to the FT's so the air coming out is slightly warmed up. I figure every little bit of warming helps.

Not sure what page it is but its in my IBC AP thread below

A 4C drop in the temperature for a 1000litre FT is over 4.5kWh worth of heat removed from the system. Overnight, say 12hours (you dont mention exactly how long it took), that's an average rate of loss of 375W, so a 300W aquarium heater wont quite keep up with the loss, but it would have limited the temperature drop to ~1C.

The heat capacity of air is miniscule in comparison with water (something like 1/4000th from memory without looking it up), so unless you are pumping a lot of hot air through the FT, it wont have a huge effect. Quite a bit of heat would be lost to evaporated water too.

Now, assuming I've worked this out properly in my head, even with 100% heat transfer efficiency with no losses (it's not going to happen!) 1000l of air, say 20C above water temperature, bubbled through 1000l of water is going to heat the water by... bugger all!

The tank has a layer of black plastic, old carpet, inch thick hard foam and a bit of the silver and foam roof insulation from the roll. So its well insulated so I cant figure how it would have dropped so much so it must have been the air pump putting the cold air through. (all the beds and sumps are insulated to). Ah well lucky reprieve for the fish couple of extra months of life..

On a side note put 5 of the smaller perch in with the gold fish to see it would make them less skittish because the goldfish used to wait at the surface for me when I came in... haha they haven't done that since dunno what the little silver bastards told them

Well I stick to my thoughts that every little bit helps and my 2 or 3 x 3 inch airstones in each tank pumping warm is at the very least got to a little be better than pumping cold air.

Conversely if you sit in the hot tub on a hot day and turn on the air blower youl feel those cold bubbles on your bum

I think the most important factor over all is having as much of the system insulated as possible to slow the heat loss rate.

Then add every little easy low cost option you can to produce even small amounts of warmth to your water.

I went around and painted all of the PVC piping that gets full winter sun black today, I don't expect this to contribute a great deal by itself but it only cost me about $2.00 worth of paint and took 1/2 hr so the small amount of warmth it will add seems like a good little return on the investment to me.

Another easy one of course is to store your top up water out in the sun and only top up in the afternoon when that water is at its warmest.
Last winter using a small pond pump I ran my top up tank water through our30M black garden hose that was spread out on the drive way all day on the week end then topped up my systems in the arvo there was several degrees difference in the temps. adding 100+L of warm water has got to help

hahah yeah all the focus on keeping the warmth in has seemed to only keep the coolth in and the warmth out through the day. I might try making a hot box with a coil in it if I get time around uni. As long as I don't lose fish its all good. I thought I read that silvers start dying at 14 and today it was sitting on 15 so I'm starting to get nervous.

Air in small volumes just cant shift enough heat to account for the energy transfer you saw.
All that exposed area of clay balls is radiating and convecting heat away when the air is cold, it is surprising how much heat gain and loss there can be, especially if it is wet. 375W isn't a lot over a few square metres of exposed surface, you'd barely notice it.

I have about 6000l of water in my system with the tank and sump buried in the ground, and 8 out of 9 GBs in a greenhouse, with much reduced water pumping time at night, and lost almost 4C overnight with the cold change- thats almost 28kWh worth of heat.


Specific Heat of air = ~1.2kJ/m^3.K @20C (1m^3 of air weighs about 1.2kg, and the S.H. is 1.005kJ/kg.K)
Specifc Heat of water 4.18kJ/litre.K

Roughly speaking, to heat or cool 3500l of air by 1 degree requires as much energy as heating or cooling 1litre of water by 1 degree.
You have a thousand litres and 4C change, so that's the same energy change as heating or cooling 14 million litres of air by 4C. Lets say the air was 10C cooler than the water, and there was a 50% efficiency (figure plucked from the air, I don't know what it would be in practice, but it's not orders of magnitude out) in the exchange- you would have had to pump a couple of hundred thousand litres per hour through your tank to acheive your 4C temperature drop.

Anyway it's late, I'm tired, it's way past my bedtime, and too late to be thinking about thermodynamics
That sounds too much, I'm sure someone will be along to point out any errors I've made.

pretty easy to make a solar heater. black poly in a coil with a thermostatically controlled pump it will work with or without an insulated box.

if you are desperate maybe an immersion heater like a kettle? careful or you may end up with poached fish.

how warm does it get in the tunnel? I would have thought that it should get reasonably warm?

maybe switch off the pumps during the night or time of extreme coldness?

Whatever insulation will keep the heat in.

The fan works because as water evaporates it absorbs heat to help with the state change from liquid to gas.
Blowing hot air over the tank water will do stuff all, other than make your meter spin.

A 300w aquarium heater would be more efficient, cheaper, and slightly less useless.

I was wondering about using it on the airpump to put it through the tank.

Didn't think it through in terms of heat capacity of waterversus the air. I'll definitely look into building a little hot house with a coil running through the day. But firstly might have. To plug an air gap we left at the bottom for ventilation. It backs onto a colourbond fence which is running pretty much north west to south east and the top of the tunnel is ovoid With the highest point sitting just above the top of the fence line. So as a south westerly blew over the fence I think that it might have made a pressure difference which sucked air through causing a draft over the gb's.

P.s. Thanks heaps for the help. Its got me thinking along much better lines