Ulcer

http://imgur.com/a/j1yAn#72OYC In the link above are 5 screenshots showing how multiple levels of the Well Tower can stack its effects for improved results. I noticed this is only possible if done manually, and if applied with higher levels first (Fountain Tower, Spring Tower, Well Tower). Higher levels will take priority when autocast, and will override lower levels. Jinx and Hex Towers do not stack, but Erosion and Corrosion Towers do.