I noticed some light orange colored flash rust towards the back of my tank while the sending unit is out for a week. i had a ceral bowl covering the hole. the spot is about an inch high and 3 inches long. but i cant reach there inside to clean it, will it hurt anything if left there?

 

i doubt it. The sock will block it,and if any gets through you still have your other filter. I dont think it would hard the pump its self. there is always that possibility though.