AusBonsai

I've noticed some organic pellets that I place on the surface grow some kind of mould around them. This usually happens overnight after watering and the sun kills most of it off the next day (depending on how exposed the surface is exposed to sun).

I'm mostly noticing this on the Charlie Carp pellets and much less on others.

Anything to be concerned about that could damage the trees?

Just part of the decomposition process. Nothing to worry about.
What's in Charlie Carp pellets?

I can't find much other than the chemical breakdown listed here: https://www.charliecarp.com.au/wp-conte ... 9-7-18.pdf

But I believe it's meant to be pretty much only whole European Carp processed into pellets? I know very little about fertiliser manufacturing.

Agreed that it's likely just the standard decomposition process, just can't be too careful especially when Rooster Booster doesn't have the same effect.

Just normal decomposition of organic matter so it should not harm the trees.
Charlie carp pellets should be pretty much dead fish. Analysis shows 6.7 - 1.37 - 3.74 so they should make plants grow.

BonsaiPancake wrote: ↑November 3rd, 2021, 2:10 pm I can't find much other than the chemical breakdown listed here: https://www.charliecarp.com.au/wp-conte ... 9-7-18.pdf

But I believe it's meant to be pretty much only whole European Carp processed into pellets? I know very little about fertiliser manufacturing.

I notice that they claim ''organic BASDED'' fertilizer. That means there's more than just fish. It could be they added chicken manure (most pellets have it) but going by my experience with their liquid, they probably have added potassium chloride (although I notice they don't include chloride in their ''analysis'') Potassium chloride is the cheapest and nastiest form of potassium. I hate when fertilizer manufactures don't tell us what's in the stuff they sell. The dumbing-down of the horticulture continues... Seasol is the same with their ''hydroponic fertilizer'' Basically they say ''trust us, it's what you want. You don't need details''

BonsaiPancake wrote: ↑November 3rd, 2021, 2:10 pm Agreed that it's likely just the standard decomposition process, just can't be too careful especially when Rooster Booster doesn't have the same effect.

Rooster Booster pellets also get the same fungal hyphae, particularly when they are mounded rather than spread out like in your picture.