Is that an under gravel filter? Most of your plants look aquatic to me. Ludwigia, bacopa and A. reineckii, I think. There are some on the left that I can't really make out. Did you remove the lead and any rock wool when you planted? Stemplants should be planted in groups of no more than 2-3 stems at a time. some even plant stemplants individually. The distance between stem groups should be such that light can penetrate to the bottom of the plant. The close bunching of multiple stems will lead to bruising and eventual decay.