Yep. Fish tank heater isn’t hot enough. I use a 48 quart picnic cooler to hold a water bath, then drop a 1000 watt bucket heater into it hooked up to a digital temperature controller with a large fish tank pump pumping water over/through the heater and a secondary smaller tank pump to generally circulate/mix up the water bath. The controller can monitor/control the temp to within 0.1 degree Celsius and can be used for heating or cooling (its programmable) over a massive temperature range. Set it to 20 for bw, and 37.8 for Flexicolor C-41.
The bucket heater was about $50 if I remember correctly and the temp controller was about $30. The two pumps and various tubing odds/ends was less than $30 and the cooler was $15 or something. Super precise and has taken a lot of the variation out of my process.
I use Paterson tanks, so for agitation I’ve thought about taking a skinny metal rod with a t-bar on the end, sticking it in a drill then sticking that into the tank where the twiddle stick goes. Set the drill to the slowest speed it’ll go, and at the agitation intervals, hit the trigger for 1-2 seconds, hit the reverse, then hit the trigger again for 1-2 seconds. This would allow for pretty consistent agitation and the tank could stay in the bath for even more consistent temperature. I’ve not done the drill part just yet, but it’s an idea. Rolls would probably not be a problem, but not sure how it’d go for sheets with a Mod54.