Just an update, I was getting 34c from the two 300w heaters overnight. It made a big difference to me on my working day.
I have now bypassed the thermostat on both, yesterday my 400lt tank overnight was 60c. I do live on the coast with a lot of bird poo and it comes off much quicker. when I got home after working from 8am to 3pm my tank temp was still 50c not bad for the price of just dropping two elements in your tank !
the price of electricity per night for 8hrs 600watts ??
not bad surly ?
Was going to ask you how was it making a big difference to your working day, but on the coast says it all, it does surprise me that you are getting 34 degrees from 600watts of heater in 8hours, how much water is that because according to the water heating calculator it would take 36 hours to get 600 litres to 34degrees from a 5 degree start and that doesn't allow for the heat loss over that time.
Water Heating Calculator for Time, Energy, and Power
https://bloglocation.com/art/water-heating-calculator-for-time-energy-Water Heating Calculator for Time, Energy, and Power The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required. Only input whole numbers, do not use a comma or point.