I'm sure you're aware that an aquarium chiller is very expensive. Over 25 years ago I had a reef tank with MQI lights that I couldn't keep the temp down on and I wound up using the compressor unit of a water fountain -with some help from a very handy friend. I can't recall how he configured it but it worked for a couple of years until the compressor died from overuse. At this point there were T5HO options that didn't heat the water so badly so went with those and fans. The next time time I used a mini freezer and drilled through it and ran loops of thin poly tubing (scores of loops, as much as would fit inside, and you want the least insulated tubing you can get your hands on) that the aquarium water would flow through. In this case, the biggest issue was the freezer running constantly and I feared this would shorten its life. Slowing down the water flow helped a ton, so if you take a DIY approach, keep in mind that less is more as the speed the water goes through is concerned. I didn't document it so don't recall how long it took, but it still burned out from running so much.
Having DIYed 2 chillers now, my inclination would be to spring for something designed to chill water rather than try to build a better mousetrap. Restaurants are closing right and left these days with Covid, if any places around you had a lobster tank, there's a ready-made chiller on those if you can spring a deal.
Nothing good happens fast in an ecosystem.