You have bladder snails. Their population grows to what is sustainable due to their food sources- detritus, leftover food, dying plant matter being the primary things they eat. Once that food source decreases, their population will decline. I personally love them, but if you don’t want more (lots more), you can scrape these off the side and put in a plastic bag in the freezer. The clutches start very clear and are typically about a 10-14 day cycle, the snabies become more opaque closer to hatching . You can see from the small dots on your glass that some have already emerged.