My roots were getting tangled behind the air tube connecting pump to diffuser (I use the bigger 9mm tubing) so make sure it's not that, the pump was causing the water to flow in the direction of the air tube so I think roots were just wrapping behind it and getting caught, make sure your tubes are clear
Good going on the reflective material, you can literally cover the whole bucket with that if you have enough. I used some flexible polystyrene from my LED packing and taped it around the whole bucket, saves you 2-3 degrees and stays cooler for longer but yes proper insulation is gonna do the best job. I also had a small fan blowing across and under my air pump to help keep it cool, nothign drastic but every little helps 
