It leaches chemicals into the water, does not last as long as copper, rats chew through it.

If the cleaners use the proper chemicals and the mold returns (and there are no leaks, drips, and adequate ventilation), call the mold ghostbusters!

If the chemical balance is maintained, it will stay clean.If guests stay for less than five days, your tub should survive long enough for you to balance the chemicals again.

At the time when the chemical industry discovered farmers as a huge market all sorts of herbicides and pesticides (the are banned today) were introduced, stored and disposed of basically into the ground: the farmer did not want to have stuff growing between the barn and the farmhouse anyway, so seemed like a good spot to kick that barrel over.

And the moment someone discovers toxic chemicals in the ground on a property you own the value will plummet b/c no one will want it. 

I know in New Jersey, you cannot bill if you clean it yourself outside of the actual chemicals used (I.E. free labor).  

Try these options before busting out the heavy duty chemicals.

We agree with @Travis BiziorekBay City, Saginaw & Flint all have low price points, but little to no growth.There are better opportunities in Detroit, even Midland (home of Dow Chemical).

Then buy the proper chemical to spray on that will take research to figure the proper type  .

My housekeeper drains my hot tub after each guest and replenishes it with water and chemical that they provide.