Please Help! Brown spots on clownfish

[ChloeB]

I have two frostbite clown fish, which i had for about 2 months now. I received them from a another owner who could not care for them at this time. Ive notice some spots on the head but I figured it was nothing because it was so small to see. But I woke up this morning to see the size of the spots on the head growing bigger. Please help me identify what it is and the treatment because Ive come to really bond with these fish in the last two months.
Fish are acting normal, no heavy breathing and still eatting regularly. They eat frozen brine shrimp and occasionally fish flakes

Water condition:
Salinity:
Ph: 8.2-8.4
Nitrate: 10-20 ppm
Nitrite: 0
Ammonia: 0-0.25

 

[Tamberav]

Hard to see but clowns can get hyperpigmentation from rubbing against their nem's.

 

[ChloeB]

Additional photos