I have 2 clown loaches and one zebra loach. All three of them like to hide behind the heater in the corner of the tank. Is that normal? Also whenever someone walks by the tank they swim back to that corner to where the heater is. Is it normal for them to get startled like that? And I noticed when I turn the light off in the tank they swim around more. Also my zebra loach sometimes likes to chase around the clown loaches and maybe just nip the back of them. Not like take a part of their fin off but just poke them. Are all these things normal for loaches? Sorry for a lot of questions. Thanks.