@jtimothya
Don't
see why a mixture of frequencies should be better. There was a graph
posted in the DIYAudio thread of cleaning efficacy vs frequency. For
gaps the size we see on records, 40KHz is only marginally superior for
the largest gaps, and quite inferior for the smallest. This mirrors my
experience.
IMO, 40C is low - only a touch above body
temperature. I often start a session with a temperature in the low 40's,
but continue to begin 15 minute runs until the temperature hits 47C,
when I wait for the chemistry to cool a bit. I acknowledge that it can
be disconcerting to see your vinyl come out of the tank a little warped,
but with uniform cooling in the rinse stage, the warp disappears. At
least in my experience, by my standards. I use a 60RPM Vinyl Stack and
running purified water for rinse.
Are you sure that your
thermometer is accurate? And that it is monitoring the relevant
temperature? Stir the chemistry vigorously - if the temp reading
changes, then your tank is not homogenizing the chemistry and hot spots
or cold spots may emerge with use. That could be affecting your
perceptions of appropriate temperature. Hope that helps.
It's not just about size.
What particle sizes do "we see on records." ? I don't think there is a univeral range.
If audiogon allowed posting pictures I'd do that here.
Take a look at the graph on p.16 of this PDF:
http://www.idema.org/wp-content/downloads/1622.pdf
This is about cleaning perpendicular magnetic tape but it should give you a basic idea.
Also take a look at my article here:
https://thevinylpress.com/timas-diy-rcm-follow-up-2-compelling-changes-improved-results/There is quite a bit of information on the Web about use of multiple frequencies in USC. Don't
just
stick to threads about record cleaning, there is a ton of junk information to sift through in audio forums. We are still learning, mostly from trial and error, but the technology has been in the industrial areas for quite a while. Here's one example about particle size and frequency; you can find more with a little research of your own:
https://techblog.ctgclean.com/2019/09/micron-size-vs-frequency/Wrt temperature, there is a relationship between solution composition, heat, and cleaning efficiency. Wrt VersaClean, what is the TDS ppm using that in solution? I prefer high purity IPA. PhotoFlow is not recommended - a little research will tell you why.
Of course, people can do whatever they want based on what they believe. I'm only passing along based on my experience and research.