Advice on water chillers please.

Gph is gallon per hour (how much water it will chill to its max) watt is how many watts you burn in electricity and btu british thermal unit is how much heat a unit can push or extract. You want enough flow to accomodate your needs (pipe size and pressure plays into this as well) xwatts will tell you roughly how big the unit is like 1000 watts run every hour is 1kw/hr sometimes what you will see on your power bill. Btu needs to be big enough to accomodate your ideal temp to keep up with flow. By the looks of the question gph vs btu are similar values in different formats/formulas. Good luck. Its math.