Because the tap water in our area is extremely heavy in calcium, our faucet filters calcify quickly. I regularly remove all the faucet filters in the apartment and soak them in vinegar overnight, but the filters in the bathtub are so encrusted that I can't remove them.
The bathtub has three regular faucet filters in a row that are thoroughly calcified - so much that the amount of water passing through is not enough to trigger the hot-water heater to turn on, thus resulting in cold bath water :-(
How can I de-calcify these filters without removing them? Or what can I do to remove them without destroying the bathtub inlet?
It doesn't help that the tub's filters are very inaccessible so I can't get a proper hold on them with any tools. I'm also afraid that the plastic parts might be damaged.
front view: 
view from below:
