Betta Fish: Need help identifying this thing in my fish tank glass

Guys I need help to identify what is this kind of white thing attached in the glass of my fish tank.. It looks like eggs or something but from where? I just did water change now so it's not visible in my tank anymore..Inside the tank is 1 betta fish only in a 5gallon tank with heater, sponge filter, lights, live plants and substrate is pebbles .. Temperature is 80° Fahrenheit.. PH is 6.8.. Ammonia is zero, nitrite is zero and nitrate is zero also before water change. Just some of the plant leaves are melted which is also confusing and I saw one white thing like worm wiggling during cleaning the substrate..Is this thing in glass dangerous for my betta and that wiggling thing as well.. I set up this tank August 1, I put my betta August 20 so its 1month today since then