My brand new Dolphin Wave 100 pool cleaner has a hard time climbing the walls to clean the waterline. Specifically, it looks like out of 20 efforts it may manage to climb the wall once. I am certain that the filter is clean because we clean it essentially after every use.
The local distributor has thrown an idea that the reason may be a thin biofilm on the walls (algae precursor??) that makes the walls slippery (the pool water is otherwise crystal clear)
Does that explanation hold any water?
Let me also add that a different pool cleaner from Astral that we tried, did not have any problem climbing at all.