Stains or growth in hot tub. What is this?

[jamesg5000]

Hello

For the last few months been seeing this appear in my hot tub. Reddish brown marks. Seem to like to be around jets or in corners. Wipes off ok. Anyone know what this is?

• Chlorine tub
• Chems are balanced
• 10 year old Lucite tub

[Scottie_In_IA_1981]

I can't really speak to this from experience, but I do have some thoughts.  

If it simply wipes away easily, then I wouldn't think that it is either a stain or a growth.  From the picture, it looks like a dark reddish brown color...which, probably isn't too far off from what a rust stain might look like (again, I can't speak from experience), but if it was rust I wouldn't think it would just easily wipe away like that?

The one thing that it actually reminds me of is pollen.  The only reason that pops into my head is because of the time of year currently.  Where I live, there is some kind of chalky dust like pollen that gets kicked up...it's very fine, and the only time I ever see it is when I walk through the grass this time of year, it's like it settles into the grass and coats it, you can't really see it just by looking at the grass but all it takes is a walk across the yard and when you come inside your shoes are covered with this fine reddish brown dust.  You would think that your filter would remove pollen, but the kind of pollen I'm talking about is extremely fine and basically invisible until it 'collects' somewhere (like the grass, or on a pair of shoes)...so, the pollen I'm describing is obviously something that could easily be blowing around in the air, and even if your filter did a good job filtering it, a tiny bit could probably still get through and remain in the water.

Did you notice it before draining the tub?  If you're pretty sure that it wasn't there before you drained it, but then noticed it after draining and having some time to dry out...pollen would make sense, because before it was simply floating or suspended in the water and you wouldn't see it, and it wouldn't be until after the water drained and dried up that you were able to visually notice some areas where it had 'collected'.  Also, those slight depressions in the surface around the jets look like a spot that it might more easily 'collect' like that.

Anyway, I can't say that I'm correct, but that may be something to consider.  And, if that's all it is (pollen) and it wipes away easily...then it's definitely nothing to worry about.