Snail shell discoloration

[Ponzu]

Hello. I have a 3/4 gallon shrimp jar populated with shrimp and snails from this site. The jar has been going for about 2 1/2 years. The inhabitants have been multiplying, but I am concerned there may be something wrong with the snails. The ends of their shells are pale in color and have bits of algae growing on them. Is this normal? It is more prominent on the larger snails. I'm worried their shells are dissolving in the water, but I used aragonite sand when I set up the jar so I thought that was supposed to provide enough calcium. Should I do any tests on the water quality? Thanks for any advice.

[Varanus]

Shell coloration can vary, and its normal for algae to grow on them if conditions allow for it. If they were low on calcium then the shell could become pitted, fragmented and broken on the end, etc.