Awe, JM... I'm very sorry about your losing Piggy. I know it's heart-breaking... we do get very attached to these little creatures.

It's hard to see exactly what it was on his head... but if I remember correctly... a fish doesn't really die from fungus... but from possibly underlying causes for the fungus.

The medical experts here are more knowledgeable than me about this... but I'm wondering if this was flexibacter. Flex looks like wet cotton. This can kill... and can be correlated to poor water params. This link to the flex article is in the betta forum... but I believe it's applicable to all freshwater fish.

The experts will be able to offer a more educated comment but this may be a consideration.

Swim free little guy...

Michele