Depending on who gets in the hot tub, can drastically change the water quality.  1 person that has been out hiking through the park, sun tan lotion on etc that jumps in a hot tub, can leave enough organic matter that will use up the chemicals as perhaps a couple that uses it every night for 5 days, but they jump in clean and aren't doing the wild thing.  

Over time, the synthetic slate products made of different plastics and polymers will begin to fade and look less like real slate and more like real plastic.

Many of the chemicals they use to cook meth are very toxic and in the people's republic of MA, you might be required to spend thousands of dollars to clean it up.

Superpaint and/or Duration are good unless you need something to fill in cracks, then you can move into something more commercial-grade, like an elastomeric, block filler or even epoxy if that is the look you want but, careful, the thicker and more commercial the product, the tougher it is to get off if needed in the future and anything not water based, be prepared to toss out or clean with a chemical and not ever use it for a water based product again.  

You can go with the chemical treatment which is cheaper to get rid of them but you have a greater chance of recurrence.  

Divide the building with a wall, front half cabana bar, put a side door in to the back, 5' wide, from the door you'd have a vanity, then toilet then shower, last 3 feet a full length sauna. toilet, Outside on the back wall put a rack and cabinet for pool equipment and chemicals.

These new systems are so advanced, and they are sensitive to chemicals, such as bleach.

It's not so complex of a chemical reaction to not understand the concept.

Was there any discussion about the chemical remediation techniques that popped up a few months ago?

Yes, the janitor's buffer is the equipment...with the proper pad and chemicals for stripping, and proper wax and polishing pad for getting the high gloss back.