I see new growth turning brown and crispy, so either not enough water or too close to the lights (too hot). Your watering schedule should be "whenever the plant needs water" as opposed to "once or twice a week," but on average how often will depend on the type of soil you have under that top layer. If it's all like the top layer, you could probably water every day or every other day just fine. If it's dirt, you'll have to stick your finger in and see how dry it is until you get more familiar with what it needs.
If you don't see roots coming out the bottom and your soil is rocks, then it's not interacting with the water in the tray underneath. If it's soil, it could be absorbing some and sitting oversaturated, which isn't good.
Edit: misread about the roots. I still vote underwatering/too hot