general questions.

Adding rocks to the top of pots to reduce water evaporation is a common practice and generally okay. However, you're correct that it can potentially create a moist environment that might harbor mold. To prevent this, make sure the rocks are clean and allow the soil surface to dry between waterings. Good ventilation and proper watering can help mitigate mold growth 400W light at 60% intensity should be okay at 20 inches, but it's essential to monitor your plants' response. If they start showing signs of stress like leaf burn or stretching towards the light, you may need to raise or lower the light accordingly. The goal is to maintain the optimal light intensity for your plants without causing any harm.