Neon Tetra issues

Question
Hi, I have a tank approx 70 litres and i am having issues with my 9 neon tetras, they seem to be huddled close to the heater/filter at the bottom of the tank - i was told this is not normal for them as they should be middle to top swimmers, i also have 4 black neons and 5 orange neon tetras (unsure if this is correct name) these are fine, they feed well and stick to the top or middle of tank - its just the standard neons they will not move from the heater.filtre, the neons feed well too its just they will not move. the temp is set to 25 degrees celcius and as far as i know the correct temp, as i said the other fish are fine. any info would be appreciated. kylee

Answer
Hi Kylee,
Is it possible there might be a bully in the tank that's intimidating the neons? If not, are these neons a recent addition? Maybe they are still shy and taking some time to adjust to the new environment. If that's not the case, I might think that perhaps there is a current in the tank that the neons don't appreciate and they have found the quietest part of the aquarium where they are most comfortable.

Best wishes and happy fishkeeping!
Karen~