Hello bonsai empire forum,

First time poster here, seeking some sort of explanation to a strange situation concerning a fertilizer that i have been using. I have had my bonsai for the last year and a half and have had a mostly positive experience with it. It is a Serissa foetida, and i bought it from a bonsai store near me and with it i got a free bottle of fertilizer (a picture of which i will attach).
At first this fertilizer seemed fine, and so did my bonsai, but soon later i found what seemed to be a white mold growing on the top layer of the soil of my bonsai, which when removed quickly returned, and as this mold grew my bonsai seemingly got weaker and lost leaves. Soon i noticed that there were some sort of grey particles floating in the fertilizer that weren't present when i bought it. i was so curious that i put it under a microscope, and what i saw seemed to be some sort of organic tendrils (again, a picture of which is attached below). after this i stopped applying the fertilizer and soon the mold stopped growing back and my bonsai returned to health
So this is my question to you forum, what is this strange contamination in my fertilizer? is it natural? is it what was harming my bonsai? If anyone has any knowledge on this subject i would be extremely grateful if they would share their knowledge.

Cheers for reading,

FLOTUS1.