Water cooling help?

https://preview.redd.it/dpibpe1a4bah1.png?width=608&format=png&auto=webp&s=096bf4b19030f004e3032434fc72420c9f376e1f

Ignore my messy piping. I was trying so many different ways to do this... things got a little out of hand lmao.

Question:

How do you make it so the water doesn't leave the loop until it reaches your desired temperature. I can let it go in at 80 degrees and leave at like 50-60 degrees without significant alteration. But I want it to stay in the loop until it reaches 20 or lower. That means cycling over and over inside until it reaches that temperature. What do I need to do to get that to happen?

I fumble with automation. As stated above, I tried a few different ways, but to no avail. It always just clogged it and stopped the rotation.

Any notes?