Red algae or coralline algae.

[prisse67]

This stuff is dark red can’t tell if it’s dark coralline or bad algae. Tank is over 2 years old parameters all in check.

 

[vetteguy53081]

Looks very much like coralline. One way to confirm is to blow with a turkey baster. Algae will move or blow off. Coralline wont

 

[JGT]

Its very specific rather than a general coating so that leads me to think its coralline.

 

[RedReefer]

Coraline, as @vetteguy53081 hit it with some flow and see if it stays.

 

[rd62rdstr]

I’m getting similar in my 29g, will try the turkey baster idea.

 

[Uncle99]

Coralline algae is of the reef building type and is hard and encrusting.
If it comes off easy, it’s just pest algaes.

 

[prisse67]

Thanks I’ve been at this almost 3 years I’ve really come a long way but I love this community because sometimes you just need that extra help thanks for everyone’s input really helpful.