Tetra Cool Fan / Built-in Thermostat for 30-60cm Tanks

Tetra Cool Fan with built-in thermostat / Brand new, unused.

How about this for managing water temperature during the summer?

Oxygen Depletion:
When water temperature rises, the amount of dissolved oxygen decreases, making fish more susceptible to oxygen deficiency. Creatures that require more oxygen are particularly affected by high water temperatures.
Weakened Immunity:
High water temperatures lower fish immunity, reducing their resistance to diseases.
Pathogen Proliferation:
High water temperatures promote the active reproduction of pathogens and parasites, making them more likely to multiply within the aquarium. Aeromonas bacteria, in particular, thrive at 25-30°C, so high temperatures increase the risk of infections.
Water Quality Deterioration:
High water temperatures accelerate the decomposition of organic matter in the water, leading to poorer water quality. When water quality deteriorates, fish experience stress and become more prone to illness.

This product is currently selling on Amazon for 4,580 yen, so I believe this is a great deal.

It was opened once after purchase but is unused.

There is a small tear on the box.