I am a first-time tomato grower and decided to make it even more difficult for myself by growing them indoors. The plants have started to bear little tomatoes but now the tips of the sepals are turning brown. I fear that if they continue to do this, they will die and the tomatoes will fall off before they mature. The rest of the plants look very healthy - no disease, no blight, no insects, etc. I give them 12 hours of flourescent light and two 30-minute intervals of fan each day. I water them once a week (the pots are 30% mulch). Any idea what could be causing this? Thank you for any help.