Heating on tank upgrade question

[Matthew English]

I currently have a visi therm 400w heater for my 375 litre tank , my new tank will be 600 litres, can i buy another 400w so there's 2 400w heaters In the 600 litre tank, or would that be to much,

So would 2 300w be better, means buying 2 new heaters

Or 2 400w means buying 1 new heater as I already have 1 400w

Advice needed

 

[Matthew English]

Pics of 400w heater box

 

[Matthew English]

Front of box

 

[Rocksor]

Buy another 400watt heater and a heater controller so that they both turn on and off at the same time.

 

[Matthew English]

Heater controller ?