i have a 4 foot amazon biotope containing a shoal of pim pictus and a shoal of red eyed tetras. i am wondering why my tetras always seem to hide and hover just above the substrate. all the water perameters are perfect for this set up. i have reduced the light intensity today in case that is making them nervous. could the water turbulance be to much for them? the tank is filtered by a fluval 405, would adding a spray bar and an air pump be better for them? help please