Blagdon Affinity Ice Vent Pond Heater (50w): Pond Heaters: Pond Accessories - Buy pond equipment from Pondkeeper: Pond building made easy.
Blagdon Affinity Ice Vent 50w Pond Heater, Allows Oxygen In, Toxic Gases Out, Allows Fish to Breathe, for Ponds up to 5000 Litre : Amazon.co.uk: Garden
Cloverleaf PHEAT2KW 2KW Pond Heater with Thermo Control, Black : Amazon.co. uk: Garden
Finest-Filters Floating Pond Heater for Koi Fish Pond Anti Ice Winter 150/300 / 600w (300w) : Amazon.co.uk: Garden