After the St. Andrews incident which wiped out all the alevins, and some concerns from other schools regarding the rise in water temperature caused by a few warm sunny days, Mr. Erskine, who has been overseeing the project on Hoy, has come up with a few simple steps to cool down the tank and prevent water quality from deteriorating; here they are:
KEEPING THE TANK WATER TEMPERATURE LOW
Ideally, the tank temperature should be less than 7C and never allowed to exceed 10C.
On sunny days, the shed temperature will be higher than the outside air temperature, due to heat transfer from the walls and roof. Opening the shed door and windows will keep the tank temperature down. Wetting the shed floor and the sides of the tank will also help. Windows which are not facing North should be kept shaded from the sun.
If the temperature is very high, ice made from bottled or burn water could be added to the tank, keeping it as far away from the ova or alevins as possible. The pump should be kept running to avoid water much colder near the ice.
To calculate the amount of ice needed:
Measure the length and breadth of the tank and the depth of water in centimetres.
Multiply length X breadth X depth to obtain the volume of water in cubic centimetres.
Then, assuming that the ice is at freezer temperature of -18C:
Divide the volume by 98 to calculate the weight of ice in grams needed to lower the water temperature by 1C.
V = L x B x D
= 60 x 40 x 20
= 48000 cubic centimetres
48000 / 98 = 490
Add 490 grams of ice to lower the temperature by 1C.
Once all the ice has melted, another batch could be added. Try to lower the temperature in 1C stages to avoid thermal shock.