do record cleaning fluids soften the treble?

Most of the cleaning solutions can't be removed completely, mostly based on the Design of RCMs. Point nozzle is the winner here.
In combination with a cleaning fluid which has parts of soap in it, this will be the written result. Other cleaning fluids have chemicals in it, which "smears" the vinyl, reduces the noise and so on.

Doug, Your logic appears reasonable but the results don't agree with what I hear with my own ears.

Fortunately, everyone is free to make their own conclusions about record cleaning. What works for me is very simple---I only clean records that need cleaning. To my ears the "uncleaned" record usually sounds better, so why subject a record to cleaning if it doesn't need it?

The very word "cleaning" implies that cleaning is an improvement. But maybe other things are going on than just cleaning. People get hung up on whether cleaning fluids leave a residue behind. Maybe the concern is whether they remove something from the record surface that actually contributes to the sound quality.

The why behind all this is really not terribly important to me. I have no interest in exploring the chemistry of records or cleaning solutions. All I want to do is enjoy the music on my records, and if someone wants to call this distortion, that's ok. After all, I listen to records on an all-tube system; maybe I like distortion.

Dave

Only if you gargle with them.

All very well but I just listened to "Music From the Time of the Crusades" on Argo; I gave up half way through one side before I cleaned it, really noisy. After cleaning it was much better and sounded fine to me. It use to be a general recommendation that you clean new records before you play them, I have seen several comments about how much crud was on them. Everyone to their own taste but all my friends with LP collections have cleaners and use them often.

As I mentioned earlier, if a record does not seem to need cleaning, I leave it alone. Salectric's ears tell him "...the 'uncleaned' record usually sounds better..." Time and again, my ears tell me the same thing.