It appears your photo didn't attach (or I just can't see it on my laptop). In general I'd recommend comparing what you see to pineapple sponges, hydriods or spirobid worms as those come to mind based off your description.
Apologies for the late reply, it's waterchange Wednesday in this house ;Hilarious
I have the same issue when I upload photos from my good camera- haven't figured out why that is. Pineapple sponges are completely harmless and as mentioned their population tends to ebb and flow a little for no real apparent reason. I would do ads 35ppt suggested but I would apply the peroxide with a q-tip to give you a little more control over where its applied so you don't accidentally get any on the snails flesh (I don't think it would kill them but it can't be good for them).