Are my pygmy corys glass surfing?

[Gemtrox42]

For context, I have a 30 gal tank with Current Satellite LEDs, moderately planted with gravel bottom, mostly hornwart, water sprite, swords and java ferns, lots of driftwood, lots of tannins. My fish are 15 cardinals, 8 pygmy corys and 5 cherry shrimp. I have two female lyretail mollies and one black sailfin male molly. Water is 78 degrees, hang on back filter so should be well oxygenated. Water parameters are 7.3 pH, ammonia 0, nitrites 0, nitrates 5, GH 50~75, KH 140. I am using softened wellwater. I treat the water with aquavitro seed and dechlorinator/balancer. My corys don't get a lot of leftovers, as I feed my fish sparingly, but I give them 1 hikari sinking wafer per day, which they have to fight the cardinals for. Luckily they are happy to munch on my driftwood fungus.

My corys will usually spend large periods of time in groups of 2-5, and rarely on their own, moving up and down the leftside glass in an oval-shaped pattern. They virtually exclusively do this on that side. When not doing this, they can be found on any side. I have tried changing light levels, covering the side with wrapping paper, then 3 sides in wrapping paper, and it does not seem to effect the behavior. The activity is most fervent in the mornings and evenings however. In case it helps, this is the same side of the tank that my heater and filter are on. I am unsure if this is normal behavior as I have read they like to shoal on occasion, so any advice or insight would be appreciated.

 

[Colin_T]

got a video of the fish?

 

[Gemtrox42]

Unfortunately I can't get video. Here are some pics in the moment though. Since my post I have read up and it sounds like swimming to the mid and upper tank levels is normal for them. I am going to attempt moving my hang on back filter to see if they are following the current and are just by the glass because the water flow is there.

 

[Gemtrox42]

Also, bonus question if you're up for it: my female creamsicle lyretail molly just started doing this today. She can spend up to minutes at a time here, then leaves for a while, only to come back to do it again. It looks like the shimmies, but I looked closer and she's also sucking on the glass of the heater. Could she be eating something growing there?