Most rot will happen at temps over 21c I keep mine at 19 to 20 I.e cooler turns on when it hits 20 to bring it back down to 19. You can try silver bullet to kill it off but tbh with you at week 1 just bin and go again. Or you will spend the next 2 months struggling. Also try using hydro guard you will never have a problem when using hydro guard . Also if you can invest in a good water cooler and keep the temp below 21. Sorry for your loss bro, but it’s all a learning curve.