Tips for the tomato plant sepals are turning

[IndyG]

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.
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[Kisal]

It's hard to say, without seeing a picture of the plant(s). Would it be possible for you to post one?

The only thing that jumps out at me is that you might not be giving them enough water. Tomatoes need quite a bit of water.

Or did I misunderstand, and you actually have a hydroponic setup?
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