Last weekend had to remove rear tyre due to small split. In the tyre was a coral like growth of dried stans fluid about 50mm in dia , I fitted the tyres in july so its fresh fluid, anyone else has this

Yup – I think it’s pretty common. Is it due to using CO2 to inflate the tyre, which freezes some of the fluid? Not sure.

just occurs no matter what IME

It’s when you get a flat generally. At one point it would have been attached to the hole!

It’s worth changing the sealant every few months for this reason as the bits that do the sealing aren’t going to work if they’re in a great big ball rolling around inside the tyre.

I find this happens more quickly in the Summer when the ambient temp is higher. It also seems to happen more quickly on some tyres than others.

I’ve only hacd it the once. Similar sized coral.
Noticed that the remaining fluid was almost clear too.

I’m inclined to support njee20’s theory. It’s clearly begun with something “seeding” the growth. Such as a build-up behind a puncture.