Scary fast spreading algae

Okay, so this is a weird one for me.

I had some light algae, brown in color on only 1 slow flow area of my tank. I figured this was pretty normal in a dead spot. It was underneath a glued down frag plug and I figured as stuff encrusted it would just starve out.

Test result are as follows:
Nitrate: 0 (Salifert)
PO4: 0 (Hanna)
Alk: 7.9 (Salifert)
Calc: 434 (Hanna)

So onto the hard part, this stuff is not normal algae. It looks feathery, and attaches to the rock like polyps. If you hit it with a baster, they all close up. It closes up at night. It is dark red/brown in coloration and is spreading unbelievably fast, I even have some on the sand. I changed my BRS GFO HC just to be sure PO4 wasn't false positive. I have a large fuge with a basketball of chaeto in it.

I would think false positives on the nutrient levels, but its a 90% SPS tank and all the coral has been and continues to improve and grow. I added a BP reactor about 5 days ago to see if that might help negate this stuff, and so far that has done nothing (as I assumed, needs to seed)

Any ideas what this is or how to get rid of it? It is definitely not cyano.

Thanks all.

 

Colonial hydroids?

Picture please.

 

Here's a photo. Best I could really get of it through the glass, I don't really know how to use my girls DSLR. LOL

Thanks



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Attaching a completely uncompressed one also.



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Looks like a type of red turf algae. I wouldn't think an algae would "close up" however.

 

I agree, that's why I am worried. I'll get a pic tomorrow night of the same spot closed up for reference.

 

It is difficult to say for sure but in the uncompressed photo it appears that this material actually has tiny finger-like tentacles- similar to clove polyps. Is that correct? Are they individual polyps all connected on the encrusting base? Algae will not have these structures, nor will it react to touch. I am thinking animal, not vegetable. Unfortunately, I do not know which animal.