You need to remove that plant. Looks like it might be built up gas bubbles, probably wont be good if they pop in there. I haven't seen it happen, but know it can. Could be a number of other issues, but the plastic is obviously malfunctioning and to be safe I suggest you remove it. It's not eggs, for sure. Not from betta or tetras or anything I recognize, so I assume it's a problem with the plastic.