Mini waterfall filter has heat issues

[stelim]

Over the weekend, I converted my betta tank [17cm (L) x 17cm (B) x 18cm (H)] into a nano tank. Attached a waterfall filter from C328 and a 7W PL light. I noticed that the water is very warm even when the light is off and the tank is not placed under direct sunlight. I concluded that the punp in the filter is generating a lot of heat. Do any of you have experience this? Should I get another pump?

Thanks in advance.

[e-mini]

What is the flowrate of the filter?

For such a small tank, I would try to get the smallest hangon filter or just a sponge filter.

[stelim]

I threw away the box. But it's the smallest that the shop in C328 had. I only cost me 8 bucks for the hang on filter.