How many and what wattage heater?

[1979fishgeek]

Noticed my Powder Blue Tang looked a little stressed, then noticed the tank temp was 22.5C (72.5F) it's winter and the temperatures dropped dramatically outside and this must of been the final straw for my heater. I was running two 300w heaters and now only one is working...and it's struggling.

I am just ordering another 300w but wondering if I should be running three in a 800l tank?

What's the correct way to calculate heater wattage in a tank?

For instance basic room temp this time of year is 18-20c (64-68F) and I like to run my tank at 26C (78.8F) so what wattage should I be running?

Thanks

 

[1979fishgeek]

In the mean time, I have added every spare heater I own....luckily that's several (3 x 100w to 2 x 200w) different heaters running now, sump is looking like it's being assimilated by the Borg.