Heating a fish room

[peterfc1]

As the title says how to best heat a fish room. I have one tank it's app 5,000lt an two quarantine tanks 20 lt each. The fish room is well insulated but over the extreme cold spell we had in Portugal i struggled to keep above 24c.
I have an IBC 1100 lt water container in the fish room to condition water for water changes I normaly change about 25% per month. Anybody tried using an IBC just for heating a room i could easily heat the IBC to about 30c .
Anybody got any ideas that won't break the bank.

Peter

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