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Some probes and/or meters require a few hours of 'settling in' before they'll read accurately, even with calibration solutions.
The calibration solutions I'm familiar with read 230 and 470. Chlorinated tap water should read over 500, in my experience. Mixing up a solution of 4 parts tap water plus 1 part bleach will read very high as well -- 600-700.
Offhand it sounds like you've got a bad meter/probe.
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