350 litre tank... Planning to be low-tech (Diana Walstead esque)... Use the Rena XP3 that goes with the tank... Or... Use my Eheim 2324 Thermo (backup up with an in tank heater to provide full heating capacity). Designed for up to 150ltr tanks. I favour the latter because it's cheaper to run than the Rena and seems to be more in the spirit of low-tech. It also means I only need one in-tank heater. Thoughts?