Thank you for your replies, everyone!
I've read about the white vinegar method; the thing is, we get these crusty, flaky, crystalized deposits on everything -- the plastic of the HOB
filters, the rim of the tank, the back of the wooden stand...can I use the vinegar method to clean most of these surfaces? In other words, can I scrub the tops of the filters to get the crud off as well as the other areas, and with the filters, what's the best way of going about cleaning them? Do I need to dissolve the vinegar in water first?
Is it normal for some of these deposits to be so baked on that they're kind of embedded in the material already? For example, the plastics of our filters seem to have these embedded stains from the deposits so bad, no matter how I scrub or even if I use boiling hot water on them, they reappear after a little while of cleaning them, as if they're always there, embedded in the plastic...