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The roots and stem I see look healthy. I would water when fully dry (unless you are using the semi-hydroponic growing method.) You can use a wooden cooking skewer to check moisture inside the medium:
Using skewers to determine when to water
The pot is larger than I would have used (unless you are using the semi-hydroponic growing method); with a smaller, more water-retentive medium such as this, I would pick a pot that just holds the roots. Still, the air spaces between medium particles should remain open and not clog up, so there should be air at the roots.