I did not see a filter but the water is clear and it has a skimmer basket.
Weird not to see a filtering system. Especially with all the oils skin and bacteria when people enter the water. If you didn’t see a filtering system recommend one to be installed. Was there a pool? Sometimes there on the same filter.
Nope, no pool.
photo 2 round top in front of the picture, did you open that up?
Exactly, it should look like this…
Dom.
Perhaps op shouldn’t be inspecting spas if he doesn’t know this.
Under the round cap was a skimmer basket, no filter.
^ This.
Stand Alone Spas often have the filer IN the spa itself, not an external.
Dom is right filters may have been removed and never replaced so they prob over treat it and drain once a month