ID Algae please?

About a year ago I purchased a small frag of this with a seahorse so it would have something to cling to. It was in a small ball with thick almost spongy branches...no leaves. (It is in the left side of the pic)

I was told it would not do to well in my tank. It sat dormant for maybe 10 months w/o changing. As of a month or two ago it began to turn fuzzy and spread like crazy.

I was curious what this was, so when I get too much I can frag it out for peoples fuges.

Thanks.
 
Many Codium species mimic a poisonous sponge in appearance, so few fish will eat it. You can always clip a piece in your tank and see if any of your fish will sample it.
 
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