Yellow Mold? on silicone in sump

[Reflective]

I have some stuff that is bright yellow with brown spots growing on some of the silicone in my sump. I used Aqueon Silicone. It only seems to appear on the silicone that is under the moving water, not on places that are submerged in water. There isn't a light on the side of the sump I see it on.

I used a paper towel to wipe some of it off, and it appears red/rust colored on the towel and stinks like mold.

I used dry rock and sand in my tank. I used janitor strength ammonia from Ace and Seachem Prime to cycle it. I noticed it started during the nitrite spike in the cycle.
Any ideas what it is and if it's harmful to the future inhabitants of the tank?

 

[Reefing Madness]

 

[Reflective]

No one huh? I was 1/2 expecting it to hatch into something gross :crossedlips:

 

[austin55]

I've had it on my sump since the day I filled it with water. Nothing to worry about at all

 

[Reflective]

Awesome! Just glad it's in my sump and not the display tank.

 

[Mike in CT]

Totally normal, will eventually go away.

 

[Maine Reefer]

Totally normal, will eventually go away.

How long will it take to go away? I have it in my sump and my display tank, so it is pretty ugly.