I stick my probe outside the fermenter with a strap and bang in a lot of insulating foam on the other side of the probe.
The downside: 1 to 2 degrees lower than inside fermenting temperature in the first 48 hours (ale) of fermentation.
The upside: easy to do, no risks of infection and it is...
I just came up with my regime and I have only done the first step. October I start with wheaties.
Brew lagers in winter (so they are ready in spring -summer)
Brew wheaties in spring (so they are ready through spring and summer)
Brew ales in summer (to keep up with summer and some darker things...
I've had a good run of about 30 batches, followed by a bad run of about 6 batches. I ruled out one by one all possible infection pathways until I found my fermentor was funking my beer.
Since then I have done 4 batches, progressively adding steps (including racking to secondary for lagers), and...
S-04 prefers 19C, but 36 hours is possible if fermentation was vigorous. Is there lots of ferment gunk at the surface/ edges? If so probably is going well, leave it for a few more days. If not, warm it up a bit and leave it for a few more days.
Ok, if its not temps(I agree it's unlikely)
do you use yeast nutrient?, mg seems to aid yeast health, and perhaps the yeast was a bit tired and did not get a Mg fix as usual from the mineral change.
Adding the us05 when you did may have not been too effective because there wouldn't be much...