what is the best way to keep minnows in a tank cold so they will breed

[bigfishhunter22]

I have a tank i want to put my fathead minnows in but i have no way to keep the constantly cold enough to breed i have done a lot of research and i found i need to keep the at 18 degrees f but i cant keep them cold unless they are in the fridge. the only thing i have come up with is ice but id have to put ice in there every 10 seconds and since i work all day i cant do that. anyone know of a tank i can use or anyway to keep them cold without puttin them in the fridge?
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