okay so I know every plant requires something that may be a little different from the next planet but generally speaking I seem to run into the same problem with each plant soil and wonder if there's something I might do differently. I've had several of my plants for a few years now and I've never changed the soil out because I didn't think I needed to I occasionally use fish poop fertilizer and water the soil when dry thoroughly. I've noticed on all of my plants soil surface there appears to be a rusty colored top soil that develops in a thin layer and a few of the plants I have started to attract tiny little flies . any suggestions??