I have a 6 week old 20gallon high tank with an eclipse2 hood that 3 weeks ago I added 4 bloodfin tetras as my starter fish. Up until yesterday, they were great to watch, they played out in the open by themselves and with each other. The past 2 days, they have done nothing but hidden in the plants (and they hide real well). It took me feeding them for me to actually see them today. (I was told only to feed them every other day). Is this typical behavor for these fish or could this be a sign of a possible problem?