Found an old PLC filter in my bag. Unused for years (git it for the kit lens of my first DSLR). There is strange spot on it, apparently under the front glass:
Situational awareness: this is the big spot slightly above and left of center:
Is it easily fixable (not a very expensive filter anyway, so ready to throw it away...)?
Also, are there good sleeves to carry filters, that protect them from shocks, don't tke an enormous space, and can be fitted with some silicagel (if this is a way to prevent fungus)?