Originally Posted by luluo
Did you just get it recently? Some plants will melt while they are acclimating. Also, make sure you have enough light for moneywort. ETA: I did some searching and it says 2 watts per gallon or more.
As luluo had said, some plants will melt while they are acclimating because a lot of big chain store grows there plants emerse, above the water line, so when they become fully submerge their old leaf starts to die off, if this is the case then the best thing to do is to clip off the dying leaf and allow new ones to grow, I'm not sure if Moneywort works this way, but almost every plant does.
If that isn't the issue then maybe its your lights. And the watts per gallon rule is an old means of light measurement that has been long thrown away because it is inaccurate as there's too many types of lights out there, incandescent (bad for plants), T12, T8, T5, etc. Maybe the best way to address this issues is to ask, What is your lighting fixture?