What do I do now?

Most 'stem' plants have root systems that do not stay viable very long in a planted tank. Your Cabomba is an example of a stem plant. I am unfamiliar with the name 'Mint Charlie'. Do you know the proper name for this plant and do you think it fits into the stem plant category?
I mentioned the root systems of stems because unless they are pruned and replanted, IME they start to decline in health and appearance over time.
For my stems, I cut off about 4" or so of the tops, pull the rest of the plant(the base) out of the substrate and plant the tops where I've just pulled the roots of the others out. This method will maintain the status quo of the tank.
If I want to propagate/cultivate to increase the quantity of plants, I will do this in one of two ways. Either cut the stems into sections and plant them after pulling the root/base section which gives me twice as many plants, or cut the plant in half and leave the base in for an extra week or two and plant the tops next to it.
In my ten with similar light/CO2 to yours, I find that the roots of my Ludwegia Repens only support the tops for a few weeks an then need to be replaced. That plant, in my tank will grow 5 - 8" in a week. I can cut each stem in half and plant the top next to it's rooted section. This doubles my plant mass. But after doing this for a couple of weeks the original rooted part becomes less vibrant and crappy looking so I'll take the tops off of that, pull the roots and replace them with the top. It's a constant renewal process to keep them growing at peak pace.
Location for cutting the stem itself is not critical. I think that you will find renewal of the roots is.

Len