Ph and ec fluctuations

No. Nutrients act as a buffer sure.. But with intake of the nutrients goes a lowering of the PH (not always). But Depending on the amount of Acids in your soil and what you have buffered or not. Most likely you have something Biological increasing your PH. But basically with no nutrients the PH shouldn't change really. PH of water changes naturally overtime sure.. But it's a lot slower depending on the environmental factors of course. Nutrients can raise the PH but generally a lot are geared towards lowering it. . So look towards looking at your local water report.. Perhaps you are very heavy in Calcium as calcium will raise the PH of your garden. Not all places have access to water reports but that'd be a good place to start and one of the First places every grower should be looking at..