It's a bit tough to tell from the pic but the tops look a little manky on the left few? If so, just pinch them back to healthy plant and they'll sprout from side shoots. I grew some emersed that started like that - if you want a denser clump then pinch out the top and plant it separately to the roots - you'll get two plants. As long as they've either got roots and one left joint or two leaf joints and no roots there is enough to grow.
Not sure what you mean by shrinking The ones that are going dark/slimy - they won't recover so best to nip them off so they don't encourage mould and it will grow new ones. Leave any leaves that are healthy looking as they'll be fuelling the growth for now even if they are submerged ones.