Sandman

Hi <span class="link_user">@Sandman</span>! Your plant was in a situation of rootbound, roots were unable to find space/air and as a result they started to rotten, I see on your latest pictures brownish roots whereas they should be white. To be honest in this situation I would start over from seed with a fresh soil, in a airy container such as AirPot/SmartPot. These containers help you to analyse the rootmass easily, they make overwatering almost impossible, and they allow roots to auto-prune themselves, preventing from rootbound. Hope this will help, keep us updated and happy growing! :facepunch: