I've converted a small dehumidifier into a damn good chiller. I still have it for a back up. Got a sweet deal on a Aqua 1/4hp for 200 and put the diy chiller in the closet. I actually swapped it back into a dehumidifier the other day when I was drying some plants.
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Op sweet setup. I've never had good luck with a non submersible pump. I had a sick setup of 8 buckets 1 1/4 pvc with a cooler in the middle of them (4 and 4).
I'm gonna build a 4 bucket setup similar to yours with pvc really soon. I'll try and remember to post a pic here for comparison. I use these fittings on top of the buckets. 1/2x1/2x1/4