Dealing with the heat in aquaponics

Aquaponics December 8th, 2010

Trout don’t like hot water, nigh, trout don’t even like warm water. From my experience somewhere around 25 degrees C and they start to struggle. It’s not actually the temperature that gets ’em, it’s the Dissolved Oxygen (DO) level. See as the temperature of the water rises, the saturation level of DO goes down. And trout are very finicky about their oxygen. So essentially it gets to the point where you just can’t get enough oxygen into the water for the trout to survive. So you have two options:

  • Harvest your trout. Last year I pulled them out from late November through to late December – I pulled the last lot out just before the xmas holidays.
  • Fight it tooth and nail (maybe your trout aren’t big enough and you want to get another month of growth in).

Assuming you’ve chosen the “fight it tooth and nail” path then there are a few things you can do.

  • Don’t pump during the day – you don’t need to. The ammonia level will rise very slightly if you don’t pump during the day, but it won’t affect the fish. Pump all night. If you are really worried about ammonia, use an air lift bio filter in the tank (see below). Essentially the growbeds are going to heat up your water, so don’t pump up to them. Your plants will survive.
  • Shade your tank as much as possible. For obvious reasons.
  • Put an old sheet on your tank, with a corner dipped in the water. This will wick the water out of your tank and evaporate. Evaporation is a cooling process – essentially what you’re trying to do is create a “bush refrigerator” or “Coolgardie Safe“. I’d go one step further and invest in another small fountain pump. During the day this pump is on and is pumping water up over your sheet and then running back into the tank. This will add extra oxygen as well as cooling the water.

I mentioned above a concept of “Air Lift Biofilter” – essentially it’s a couple of bubblers in a tube – as the air rises it pulls the water up with it, which in turns pulls water in from the bottom of the tube. So you get a bit of water movement by using the bubbler. Then what you do is you add a small amount of rocks, or some cut up poly pipe to the tube and the bacteria live on that in a nice highly oxygenated environment and do a bit of biofiltration. The water is pulled in through holes in the bottom of the pipe, and rises up through holes at the top.

Here’s a very low tech version which I threw together with scrap peices of PVC:

Apart from that, my trout are growing well, and the cool spring/summer has been kind to them – I haven’t actually had to apply any of the aforementioned techniques as yet, where as the guys over in Perth have all had to pull their trout out! Two more videos of them feeding:

And finally – the plants. This side has been pretty disappointing this year. I have been smashed by slaters, and then I had a nutrient deficiency so I sprayed with seasol, only TOO MUCH SEASOL AGAIN and burnt the crap out of my plants, and now hail. So things are a little sad (that is, I can actually see the media!). You can see what I’m up against in the photo below. A seed sprouts and has it’s leaves munched off…

And then I went and compounded the problem by putting too much seasol in my leaf feed mix and burnt the lettuce.

But most of  the lettuce bounced back really well (you can see the burnt edges of the leaves underneath those glossy ones on top).

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