Green Coralline Or Algae?

[cshouston]

My tank is still in its first six months, but remarkably lacking in “ugly stages” so far. Diatoms are gone and I haven’t had any hair algae issues. I attribute that to a long, lights-off cycling time, nutrient control, and some additional maricultured live rock I added to the base dry rock. I already have purple and red coralline growing on some of the dry rock.

However, I have also had green spots growing quite a bit over the past few weeks, exclusively in lower PAR areas. It doesn’t blow off with flow, and I can’t scrape it off. My initial thoughts were that it was green coralline that I’ve seen posted about, and that it would eventually start to turn purple with time. Yesterday, I noticed a couple of air bubbles (assuming from photosynthesis) that caused a bit of the green to tear off and eventually float to the surface. This threw a wrench into my assumptions.

Is this green coralline or some other kind of algae? Bear in mind, it grows in shaded areas, but does coralline photosynthesize and produce oxygen bubbles?

Water: SG 1.026, pH 8.2, Ammonia 0, Nitrate 5ppm, Phosphate .04ppm, Alkalinity 8.2, Calcium 440ppm, Magnesium 1360ppm

The last photo shows two of the oxygen bubbles I am talking about. The second to last photo does NOT have bubbles—it’s just the shape of the rock. The bubbles aren’t fluid filled, they’re gaseous and only in one or two spots, so I’m 99% sure it’s not bubble algae.

 

[Foothill Corals]

Looks like green cyano to me

 

[Cell]

Coralline will not blow off rocks.

 

[cshouston]

Coralline will not blow off rocks.

This doesn’t blow off rocks either.

 

[Cell]

Air bubbles will tear it off but it won't come off when you blast it with a baster or coral feeder?

 

[cshouston]

Air bubbles will tear it off but it won't come off when you blast it with a baster or coral feeder?

Precisely. That’s why I was questioning what it was.

 

[cshouston]

Looks like green cyano to me

The green cyano thing made me wonder, but I read it’s caused by high light (this only grows in low light), high phosphate/nitrate levels (I wouldn’t call <.04 and <5 high), and low flow (the tank has a lot of flow with 2 MP40s).

 

[Saltyreef]

Looks like green cyano to me

+1 green cyano

 

[cshouston]

+1 green cyano

Again, it only grows in low light, I have fairly low nutrients, and high flow. I just stuck my hand in the tank again and touched it just to triple check: no slime. I scraped with my fingernail and nothing came off. Blowing on it with a turkey baster does nothing.

 

[Spieg]

Looks like algae to me (maybe green cyano although I've never seen that before personally). Coralline wont usually grow on the sand bed like that.

 

[CCauthers]

I have a little bit of this growing in random nooks in my tank. Doesn't grow in many specific conditions, and my nitrates are 1.25. Likely green cyano

 

[ScottR]

It could be anything. Coralline does come in many colors but we primarily see only purple/pinkish in reef tanks. My tank is less than 2 months old now. It’s very purple but in other tanks I had lots of calcified green and it wasn’t really a winner. Just made it hard to scrape off and wasn’t slightly.

 

[cshouston]

I’ve never heard of cyano that doesn’t blow off and can’t be scraped off with a fingernail.
Edit: actually with some effort, bone cutters made a dent.

I’ll just watch it. I’m not worried about it being harmful, just hoping I could get a positive ID. I’ll see what the tang does when he gets back in the tank.