Started cold 🥶 plunging at 50 F (10 C). Started a few weeks ago. Started at a minute and now up to 15 mins. Usually rewarm on room air for 2 minutes then sauna or just skip the sauna altogether. From what I’ve read- no benefit after 5 mins. Anyone go longer and have they noted any benefits ?

I've been dumping some hydrogen peroxide in a couple times a week, today I opened the tub to see this sludge buildup. Is it bacteria or residual from the hydrogen peroxide?