White Growth on Rock Wool – Mold? How to Handle?

Hey there! That white growth could potentially be a couple of things. It’s possible it’s mold, especially given the high humidity and temperature range you’re working with, but it might also just be salt buildup. Rock wool can sometimes accumulate salts from nutrients, especially around the base where water tends to evaporate. Since you've already tried a diluted peroxide solution, that’s a good start. If it’s mold, the peroxide should help keep it at bay. You could also try lowering the humidity slightly to reduce the chance of mold growth. If it’s salt buildup, a good flush with pH-balanced water might help dissolve and wash away any residue. Just keep an eye on it over the next few days and see if it comes back after the peroxide treatment.