Help with neon green toadstool

[jpyatt1986]

I got this about 6 weeks ago. Also came in with a frag of gsp. It had no problems for 5 weeks but I noticed that now it has this ring around the stalk and from the ring down to where it attaches to the rock is brown. From everything I’m reading I’m leaning towards its rot. But as you can see in the pic it’s still open and extended and atleast from what I’ve read so far if it was sick and rotting it wouldn’t be happy. So now I’m wondering if I should let it go or if I need to take action.

Tank params are:
Ammo 0
Nitrates 5
Phosphates .03
Calcium 450
Mag 1350
All 10dkh
Ph 8.1
Temp is 77f
All tested with salifert kits

Tank is a eshopps deskmate mariner 7 gal step down.
153 gph sicca return
Ai prime 16hd
200 micron filter socks
Ceramic bio media
Innovative marine Helio heater

Stocked with
2 clowns
1 blood red cleaner shrimp
Neon green toadstool
Gsp

Water change is 3 cups a day
Filter sock is changed every other day

If anyone can give me some insight as to what they think it would be greatly appreciated. Thanks in advance for any and all help.

 

[jpyatt1986]

update: so I used a toothbrush and cleaned around the rock at the base because there was some algae around it and it turned out it was algae growing on it. I believe because its leaning into the flow it’s causing a dead spot at its base and guess it can’t completely shed the algae. As I was brushing the rock the brown on the base of the stock came off and the tissue under is nice and clean and matched the head. Hopefully that’s all it was