Hello, the question is how large the volume is that you want to cool. I use the HC-300 to keep my 240 litre aquarium at a "constant" 22° (even in summer). I tend to think that it is more favourable for the device and produces shorter cooling activities if it is dimensioned slightly higher than the actual requirement, so that it does not run continuously at its design maximum. In my case, the appliance switches on at 23° and switches off at around 21.8°. The cooling process takes around 10 minutes.

The simple way: how large is the volume that you want to cool down? How high is the initial temperature? What is the next higher Heila appliance level?
Assumption: For a volume of 400 litres, I would therefore choose at least the HC-500 or HC-1000, assuming that water is already being filled in from the cold water tap. - As I said, that would be the quick conclusion.

Then there would still be the physics :-): Q = c times m times delta T (Q = amount of heat, c = heat capacity, m = mass in kg, delta T = heat difference)

c of water = 4,183kJ or 4183J; with a volume of 400 litres, m = 400kg; in our case, cold water runs out of the tap at around 18° Celsius and the design maximum of the cooler is 4° Celsius, which makes delta T = 18 - 4 = 14, simply °C = K

Q = c ⋅m ⋅ΔT = 4183 J/(kg K) times 400 kg times 14 K = 2,3424,800 J (where one joule = 0.000000278 kWh )
This means that around 6.5 kWh are required to cool 400 litres from 18° to 4°. The HC-2000 has a cooling capacity of 3,300 watts (see digitec manual). This would mean that the largest HC Chiller model (which I have not found on Digitec) would need 2 hours rounded up, whereby during the cooling process the water heats up again above room temperature and the cooling process could take over 2 hours.

Conclusion: (If my calculations are correct): A Heila Chiller is only suitable for making an ice water bath to a limited extent. In my opinion, it was not designed for this application.

I hope that helps. It's been a few dozen years since I went to school.

Basics:
Cooling capacity is measured per hour

HC-130A = 110 watts cooling capacity
HC-150A = 165Watt cooling capacity
HC-250A = 265Watt cooling capacity
HC-300A = 395Watt cooling capacity
HC-500A = 790Watt cooling capacity
HC-1000A = 1650Watt cooling capacity
HC-2000A = 3300Watt cooling capacity

HC-130 / 50-100L
HC-150 / 50-200L
HC-250 / 100-300L
HC-300 / 100-400L
HC-500 / 200-800L
HC-1000 / 300-1000L
HC-2000 / 400-1500L

I don't know how big your total volume is that you want to cool. If you want to use an insulated bathtub, it may work. I use the device for my PC water cooling, but it can only cool my gaming PC to 25 degrees at full load continuous operation. If you want to cool a garden pool, I would advise against it. The performance will not be high enough.