Looks to be a Rena clone of some kind, don't be afraid of HOT hot water, if you've got kitchen gloves and a hand sprayer just wrap the plug end of the cord around a cabinet handle to keep that dry and go over it with the scrubby and the hottest water you can stand. UL requires the magnetic and electrical components to be lifetime sealed all the way to the plug.
Do NOT put it down in the sink, use a cookie sheet, plate or paper plate that hasn't been cleaned counter or dish hand washing cleansers leaving residue. (dishwasher detergent uses chemicals that most the water treatments now negate)
You'll have a plastic rod through the impeller/magnet assembly, this needs cleaned the best. Often you can't get anything through the magnet center, I keep the plastic/rubbery twist ties used on computer hardware around, give it a few twists and run it through the little hole.
A small child's toothbrush or narrow pipe brush will do a good job inside the magneto well. If you can't get the well looking really clean try warming it up with hot water then dumping the water out and putting vinegar straight from the bottle in that little hole.
Outside of those two areas the rest is "clean as much as you feel you need to" then reassemble the whole thing and run lots of tap water through it to rinse it out, you can plug it in after filling it up and get a good rinse of the impeller housing that way.
Its better to re-cycle the filter than re-infect the fish.
Your home water heater isn't capable of reaching a temperature that will harm the filter itself, but be careful of your hands, anything over 110° can harm your cuticles, knuckles and cause lasting pain. At about 114° some of the fats that are exuded onto our skin from sweat glands start to break down both on the surface and inside the glands and past 120° you're getting into capillary spasms and a risk of local or systemic shock from the heat input. Most home water heaters are hard capped at 155°F and left set at 135°F, so if you're running the water really hot pay more attention to the heat than the work, a flushed toilet isn't fun.