Fish will tend to group around the light source when you first turn off the lights. As they get used to it being "night time" they will spread out and find their hiding spots for the night. Fish like neon tetras are schooling fish and find safety in numbers. If you only have one, he sees the light as safety and may take longer to calm down and find a hiding spot for the night.

This extra stress could trigger future disease, so if you have the space get more neons!

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--->Pictures of my 75g Amazon tank<----