Help! Ich or Velvet?

[jhaun0211]

I started growing algea in my tank a couple weeks back and it spread rather quickly. Over the past couple weeks I've been lowering my phosphates maybe (.5-1) a week. It's working on the algea but I'm afraid it has messed with the tangs immune system and he's fallen susceptible to something. My other fish (clown and fire fish) seem fine he's the only one with issues. Can y'all help me diagnose?

 

[KJ]

https://www.reef2reef.com/threads/velvet-amyloodinium-ocellatum.217570
@melypr1985 @Brew12

 

[jsker]

I would suggest feeding metroplex bound with sachem focus with frozen, antibiotics, also add some vitamin C to the mix for stress and the immune system.