Angle fish sick

[Richi106]

Hey there I have attached a few pics of my angle fish which I have noticed over the last couple of weeks some marks on her. Not sure what it is.

Amonia. 0
Nitrites. 0
Nitrates. 5.0 ppm
Temp 24.8
Ph. 6.4
Also about 20mg/l co2

Tank jewel Triagon 190
Set up for 2.5 years
Standard jewel Triagon filter

2 x angles
8 x rummy nose tetra
4 x SAE

25 percent water change weekly

Fish had been in from the start.
Feed tropical pellets and tropical frozen mix

Thanks


Thanks in advance