I let FC drop to zero for 24 hrs and then brought it up to 6, but noticed I could not keep it there. Water temps are still 89-90. Dove in with snorkel and mask and found 1 little algae plant on a seat. It was a yellow tuft, but more like a miniature fern than a cotton ball. It had a stem and roots into the plaster. Probably 1/4" high. Any idea what kind of algae this is?