A few questions about jet purge and refilling

[Susanj]

When you do a jet clean,  is it always yellow gunk that comes out,  like it does when I use Ahh-Some?

 

I have cleaned off that yellow stuff at the water line a few times . Was that a sign it needed to be drained? 
 

I’ve read about wiping the shell with a cleaner before refilling. Is that really necessary? Seems to me it’d be difficult to clean it off thoroughly before refilling. 
TIA!

[CanadianSpaTech]

@Ahhsomeguy

[Susanj]

This yellow stuff stained the 5 rags I used and bleach didn’t get it out. Nor did Oxy clean. Guess it’s paper towels next time. 

[RDspaguy]

For me it was more light brown. 

Is this stuff really sticky with a harsh odor?

[Susanj]

I didn’t notice an odor ( though my sense of smell may be affected by a current case of Covid!) but it was very sticky. 
After re-filling,  what came up in the filter basket were a few pieces of what I’d expect biofilm to look like- thin irregular patches , brown colored , like a thin sheet that might have peeled off.

[Ahhsomeguy]

Hi SusanJ:  What you are describing is very typical.  Biofilms in hot tub plumbing and jets are part of a “slime layer” that is colonizing inside the plumbing, jets or even on the spa shell.  Generally, it is yellow/brownish in color and is definitely sticky like peanut butter.  After a purge you may notice additional specks that break away after refilling and using the hot tub.  If you have a decent sanitizer present there is nothing to be alarmed with.  Biofilms that break apart from the colonies and enter your water surface are called planktonic.  Chlorine or Bromine will oxidize and kill the bacteria in the film.  No worries on your part.  Just wipe any residual stickies for a day or so after a good purge.  Your filter area will collect the majority of the gunk because of the constant suction from the pump(s).