snail concerns?

I'm not sure if I should be concerned about my snails or not. I noticed when they all came to the fish trap that most have the tips of the shells eroded. I hadn't looked at them very closely in some time.

The Dimple Snail in particular has a large patch missing on its end. It was like this when I bought him (a year ago) and I liked the shell color so much I got him anyway. I don't know why the blue-green color- it looks like cyano? in the tank there is a small patch of that under substrate where a root tab is pushed against the wall- nowhere else. Is my snail carrying cyanobacteria around on its shell.

There's even some in a little crack on the side.

Erosion on snails in the tenner seems a bit worse- here's the tomato snail (Marvin I think).

and my little sun thorn Bumblebee Snail.

I admit I don't pay much attention to my snails- they seem to get enough to each from algae and leavings of peas, and they are certainly living longer than I expected. But now I think I need to give them more care. I tested pH in the tanks recently- it's 7.6 which surely is hard enough for healthy shells? I have also put cuttlebone in again but maybe they need to eat something with calcium too. I should start feeding zucchini again- I had stopped because the otos never ate it, but in my 38 I know the barbs, kuhlis and snails would all benefit. Read somewhere that you can feed snails dandelion greens and all sorts of other things too...