Water heating update

Just a quick note to record the apparent success of my little heater for the fish water.
My last post detailed the construction of a very simple black polytube heater which seems to be doing the job!!!
After about 2 weeks of operation it looks like the daily addition of just 1 degree of extra heat from the unit has raised the daily minimum temps , in the fish tank, from a low of 6 or 7 to a low of almost 10 degrees now. Still not warm but I think I am finally winning.
This new heat is a bit late for all those poor little catfish but next winter things will be better!!
Yesterday the minimum was 9.6 degrees- but it was a very cold day- it actually snowed quite heavily for about 15 minutes!! At the time Di and I were working in the chook yard making a new house for the new silkies- but that is another story.

I have also added a timer switch to the big pump setup so that the water is only pumped to the growbeds between 8AM and 8PM. The reasoning here is that the growbeds cool down during the night and so will tend to chill the water passing through them.

I have also got the differential switch working and so I don't have to go down twice a day to connect the 12V pump running the water to the heater.
Needless to say all is not quite a bed of roses- the pump draws more power than one 20watt solar panel can comfortably supply and so I have added a second 20watt PV panel.
This problem should be fixed soon as I have a mini maximizer kit which I will build and install when we get back from our little holiday to Hong Kong. This kit adjusts the voltage from the panels to enable a much more efficient conversion of the power from the panel to the load.

Winter Woes

A totally gratuitous image to start this post- this was the view I had when I wandered over to the big shed this morning to check on the fish. The local kangaroos are almost tame- certainly not much bothered by us- or by the dogs provided we keep the dogs close to us.



The period since my last post have been a series of learning experiences- most of them not good.
As we are still in winter the temperatures are still low- both outside, in the shed, and much more significantly, in the fish tank water.
My reasoning for putting the fish tank in an insulated hole in the ground were based on the assumption that the water temperature would be more stable. This has been the case. I also thought that the lowest water temps would be somewhat higher than I have actually measured.
I have been recording all sorts of details including maximum and minimum temperatures in both the shed and the fish tank water.
To date the lowest room temp over the last two months or so has been just above freezing. Night time temps have often been below 3 degrees C in the shed. Daytime temps have been as high as 17 or 18 degrees. And the daily fluctuation has been as much as 15 degrees or so.
At the same time the lowest water temps have been in the 6 to 7 degrees C range with a daily variation of less than 2 degrees. So as far as variation is concerned the buried tank works.
However the stability is a bit of a two edged sword- the tank doesn't heat up much without help from me.
At the start of this adventure I chose Tandanus tandanus and Bidyanus bidyanus species as the literature suggests that they will both survive temperatures as low as 2 degrees C. Perhaps well fed adults will but little fry clearly will not.

I think I have lost ALL of the Tandanus and perhaps another 10 or 15 of the Silver perch.

The highest numbers of deaths almost always follow the coldest days.

On a positive note the fish are still eating some Daphnia which fortunately is in good supply - they refuse all other non live food. They even reject chopped earthworms which were a favorite in warmer times.

I have even contemplated growing trout next time- however that probably won't happen for another reason- the lower temps are not only bad for the fish but also for the bacteria which are responsible for changing the fish waste into plant food.

The growth of the current plants has almost stopped. I doubt if this is due to a lack of nutrients as much as simply a medium which is too cold. I reckon that in a dirt garden the soil can soak up a bit of heat from the sun and this help the plants. My plants are constantly bathed in coldish water. Perhaps I need to do some more experiments in this area.
Having said the above- all is not doom and gloom- the peas are sort of growing. And the tat soi has a bunch of pretty flowers. The tomatoes have all been removed.

And so I tried to adapt an old hot water solar panel heater to heat the water. As the solar panel has copper pipes and connections and copper is known to be toxic to fish I decided to make a heat exchange unit to transfer heat to the fish tank water without allowing the water heated in the solar panel to come into direct contact with the water in the fish tank. As the water in the heater panel would be subject to freezing I also used a glycol solution in the system. Glycol is also toxic to fish but I reasoned that the circulating water would not come in contact with the fish water so this would be OK. I made a big loop of plastic pipe to immerse in the fish tank and tried to pump the antifreeze solution around the system. Short answer - it didn't work- too much trouble getting the air out of the system etc. And the heat transfer ability of the plastic pipe is terrible. (Can't use copper for toxicity problem mentioned above, couldn't find aluminium pipe and stainless steel tube is VERY expensive).
So I have now made a much simpler heater for the water.
Basically it is 30 meters of 19mm polypipe inside the box that had held the first solar hot water heater panel. The water is simply pumped out of the fish tank through this polypipe and back into the fish tank. Crude measurements of water temp suggest that on a good sunny day, even at this time of year, I am getting a 1 degree increase in water temp during this pass through the unit. The pump I am using is a 12volt bilge pump rated at 350 litres per hour. The power for the pump is a 20Watt solar panel , a Solarex regulator and a couple of 20Ah sealed lead acid batteries. I am now trying to fix the differential heat switch which I am using in an effort to automate the process of pump on and off switching.
My current thinking is that I might be able to keep this heater going in the summer to get temperatures which should cause explosive fish growth. And perhaps even prevent the lows of this winter by "loading" up the tank and it's surrounds during the summer. Time will tell if this logic is sound or not.

To add to the problems I am having I have discovered, in the last couple of days, that the float switch which turns the big pump on and off has stopped working properly. Actually it is worse than that - it works intermittently. With a bit of luck a little adjustment to the weights and levels of the cables will fix this problem.