Hello, I gave a 20 gallon tank. The top screen is covered in about 75% with aluminium foil. I use a heating lamp and UTH but the temperature still won't go above 85. Could it be that I use cypress as the substrate and it's about 1 inch thick? Also the thermometer is place more up top should i put it lower so it's more accurate? Please let me know how you guys keep the temperatures at 85+