I ♥ BBA!
Notice the leaf that grew in a spiral pattern. I have others that curl together. Could it be chlorine overdose? I ask because you can smell the chlorine when filling up the water and the cories become very lethargic on massive water changes (greater than 25%).
I also see calcium can cause this issue, but it is at 40 ppm, mg at 6.1 ppm, GH 7, Nitrates 40 - 80 (eek!), Phosphates 10+ (double eek!). Ever since I started dosing EI, my nitrates and phosphates are through the roof (they are already high before dosing). I am considering cutting these out of my dosing all together. CO2 - 2.6 bps (any higher and the fish stress), excel everyday. Ignore the hair algae, that's the reason for the excel dosing.