Actually, it will open usually as soon as food hits the water. Lights or no lights dont really matter. I have it directly under my lights and it is open at least half the day because i feed it often and it is trained.
I'd put it wherever it is easiest to spot feed. At least at first, i would feed every day or every other day and something meaty. It works best to cover it with a small bowl or 2 liter bottle so that the food doesnt foul up your water. Also, nothing can mess with it while it eats. Hers a pic of mine eating like that.
Try putting some selcon or zoecon in the water. That has always made mine extend so that you can feed it.
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