Why don't the suction cups on my heater (or other device) stay attached?

If the suction cups are new and do not stay attached, please make sure to clean the aquarium wall before attaching the heater. We recommend using an algae scrubber, razor blade, gift card, or other appropriate tool for wiping off any algae or debris to ensure that the surface is completely clear and flat.

If the suction cups are old and worn out, the Aquarium Co-Op heater comes with 4 replacement suction cups.