If you've had a machine producing clear ice, but the ice turns cloudy, the trouble is likely not that the incoming water is too hard. Cloudy ice can be the bizarre result of a restriction in the incoming water flow, even though the water supply is itself OK. The failure process is this: during the refill cycle, the incoming water valve is supposed to open long enough to significantly overfill the reservoir, resulting in the excess overflowing into the drain tube and out of the machine. This flushes enough fresh water through the reservoir to dilute the minerals which concentrate in the unfrozen water during the freezing process. If the water supply is somehow restricted, it can refill the reservoir, but just enough to not overflow, and each cycle results in more and more mineral concentration being retained. Eventually the concentration increases enough to cloud the ice. You don't even need bottled water to test this diagnosis; just try flushing the reservoir well with tap water, assuming your tap water isn't super-hard, and see if you don't get a significantly clearer slab for that cycle; if so, then you may have insufficient incoming water flow, and you should check the valve as described in detail above.

Another strange cause of cloudy ice is possible if you supply water to the ice machine from a water softener or water conditioner appliance that uses salt. Various problems, such as faulty regeneration cycling valves in a salt-charged water softener, can inject a dose of salt accidentally into your house water lines. A little salt in your water supply, perhaps not even enough to taste, will yield cloudy, soft ice. It is best to avoid this potential problem by plumbing an unsoftened water supply, if possible, to your machine.

The first thing to check is that dust on the condenser in the bottom of the unit isn't restricting air flow. It may seem obvious, and we've all heard the advice to clean refrigerator coils, but this is easy to overlook and happens faster than on a refrigerator. The heat exchanger coils and fins are very tightly spaced, and typically build up a mat of dust in a matter of a few months. The best way to clean them is gently using a vacuum cleaner and narrow crevice tool to suction off the dust mat. Take care to avoid bending the fins. Consider running the machine with the bottom panel removed to improve air flow and heat rejection, at least temporarily for diagnosis. I have heard of at least one case where a technician on a service call for poor performance said the machine was beyond repair and should be replaced, when in fact all that was wrong was a build-up of dust on the condenser that the owner subsequently diagnosed and fixed himself.