I am doing a university experiment on the temperature sensitivity of the growth of the early life stages of temperate seaweeds.
Currently I am using 50W JAGER Heaters in small, long tanks with a high surface area and low volume (only around 7 litres per replicate). Water is being circulated using a small water pump and the setup is under 36W Sylvania GRO-LUX lights on a 12:12 cycle at approx 50cm above the waterlevel.
I want to create several replicates of distinct temperatures with very little variation, and so far I am having a few difficulties. During the day as the temperature of the room heats up, so does the temperature of the water as it seems thermostats are only relative to ambient temperature. (I want them consistent!)
Below is the graph of my loggers, with the yellow line indicating no heater and the other lines have a single Jager heater which I have calibrated to 25 and 27 degrees. The graph shows the heaters only kept the water about 0.5 of a degree higher than the one with no heater.
I would absolutely love to know what's going on here?
Is there a way of keeping the tanks a very steady temperature that doesn't fluctuate with the temperature of the room? Do I need external thermostats to cut off the heater when it gets to a certain temp?
Please let me know if you require any more information regarding the setup, but I would REALLY appreciate any help/advice here as the seaweeds are only fertile for a little while longer and need to get everything setup before it's too late.