Over-watering is causing your issues. Now, let me define over-watering. It is not using too much water when you water. It's not allowing enough time between waterings for the soil to dry out. For the roots to remain healthy, it must go through a cycle of wet/dry/wet etc. Young seedlings might be going 7 days between waterings before they need it again. Once the root structure has set hold, watering will likely be in the every 3-4 day range in soil. Use an inexpensive analogue moisture meter to determine when to water. I've been growing for years and I still use one on my indoor plants.
I marked up your picture. The discolored clawing lower leaves tells me that your plant is not getting enough oxygen in the root zone due to being overly saturated with not enough time to dry out.
Because your plant can't move nutrients through the roots, its robbing leaves to get its MG for new growth. If this isn't corrected, it will get really bad. Soil that never dries causes acidification in the root zone due to wet muck and root rot. This in turn locks out crucial elements like Mg and CA. It's there in the mix but the plant can't use it.
Fix: Let your soil dry out until the pot is light before re-watering. Once the plant begins to return to health, cut the damaged leaves from the plant. They will never heal.
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