I have a small plant (I think) that sprung up on a piece of shale in my tank. The tank has been established for about a year with no new species introduced. It is a planted feeder guppy tank. The substrate is sand with some medium gravel mixed in. I use the tank to provide occasional snacks to my other fish and for another planted setup. There are various plants, otto cats, guppies, shrimp, and snails. I gathered the shale myself, but it was soaked in bleach and washed several times before entering the tank. There was no indication of whatever is on the rock until a couple weeks ago. Water has a pH of 6.8, NH4 0, NO2 0, NO3 0. I do use a DIY CO2 system, but not sure that is relevant. The tank is 30 gallons. I would just scrape whatever it is off, but would like to ID it so I know if there is some problem brewing.
The questionable inhabitant is an olive drab color, has forked branches, and is about 1 at the moment. It has a fine, soft texture and blows back and forth in the current, so I am not really thinking moss. The picture is hard to see, but out of 50 I took, this one came out best. I am not familiar with any algae that have forked branches, so I do not think it is algae. All the branches seem to come from a single base on a crevice in the slate. There is a small amount of green algae that grows on the top of the adjoining slate, but only enough that you can see the green tint. All plants appear healthy and grow rapidly.
Thank you in advance for your help.
