Are your water samples at the hydrometers' calibration temperature? That's very important.
What kind of filter?
A charcoal filter will not remove any minerals, sugars, etc. It may remove chlorine (and even chloramines) if allowed to run through slowly enough. But neither of those would skew your hydrometer readings at typical (safe) domestic drinking water levels.
I don't like that they both look like the bulb might be rubbing the side of the plastic tube. But since they both came up with similar readings, maybe not an issue.
Also don't like that you fill the tube completely, as I only fill enough to float the hydrometer with a inch or so below the bulb. But that is probably mostly just me.
Are these plastic Hydrometers? I've never had but glass and I wonder if the similar material of the Hydrometer and tube are causing some friction if they are touching. However the plastic probably is easier to adjust calibration if you choose to do so.
I'd think distilled water would be the thing to check calibration in when you have no other known standard. And at the proper temp.
So if these were made with you calibrating them by removing material on them, then calibrate them to what your most common pitch temp is.