The magnetic thingy would be quite tricky as the lid is too thick - it would require a humungous magnet, and if the inside brush section thingy part dropped off it would not be recoverable (and it was an option considered earlier before being relegated to the microwave files). The bubbles are a by-product of mixing the glycol with water: the tank lid areas that were not in contact with liquid as it was mixed are bubble free, and the micro bubbles are too small to overcome the tension holding them to the lid, otherwise they would travel up the slope as designed!! Options being considered are the ultrasound and a partial draining of the tank once the number of visitors drops (which at present there is no sign of happening until after the school holidays, maybe).
Experience is something that you have once you no longer need it. Sigh.