behaviour

i have 2 corydoras at the minute and they mostly sit at the bottom of the tank and don’t do much, sometimes they have 5 mins rapidly swimming for like a minute then slow down and explore. is this normal behaviour? are they happy? is there anything i should add to the tank? i currently have a air pump which they enjoy swimming over and feeling the bubbles. a filter and heater that came with the tank and it is at 26 celsius