Might be a dumb question, but im new lol and couldnt find any good pictures like mine. Basically, do you think this is algae or dirt? It rubbed a lot off with just a paper towel, some of it looks like ill have to scrub a little harder, but should come off. It didnt look "green" to me when I wiped it on the paper towel. Ive done a couple over night chlorine tests (3->2.2, 14.4->16.8, 11.6->12, yes, my last 2 test the FC went up! CC is usually 0 to 0.5), havent had a >1.0 drop or > 0.5 CC. I feel my steps are slippery (liner) (have a different thread for that!) and just want to be sure Im not missing something. Thank you!!
Most recent tests (its hard to be accurate with these colors!)
pH 7.6 (added some pH down to get it closer to 7.3)
FC 3 (I was letting the FC drift down, SWCG was at 0% for a few days, now back to 60% and FC is up near 10 now)