One area is obviously from a fish tank which the lease did not prohibit and the other is a pain or chemical stain which definitely won't come off.

The likely cause is too much chlorine or other chemicals fom the water treatment plant. 

In preparation for the party, I took down a section of the fence that was built so that they couldn't let their dogs out to poop in the yard and we also put down some chemicals that animals and children should not be near.

Would you trust a chemical engineer to build a bridge?

Furthermore, other affiliated chemical manufacturing is enjoying the lower feed stock prices as well.The RE market might soften somewhat, but I seriously doubt the bottom is about to fall out.

A flurry bought end of 21, top of 22, so they're facing a harsh(er) reality.

Or some tenants put in those dreaded bleach/chemical "drop ins" that corrode the rubber components (ruining the seal/flapper and more).

This is a flushing agent that causes the roaches to flush from their hiding places, run into the freshly sprayed chemical (I always prefered the chemical Demand CS with an active ingredient of Lambda-Cyhalothrin)It may take 2 or even 3 treatments to eradicate the problem and is not cheap if done right.

Go for dentistry (ortho or pedo), nurse practitioner or chemical/metallurgist engineer. 

Exterminator - She was not happy with the one we used and asked multiple time to get a different one because according to her the chemicals were not aggressive enough to kill the ants, spiders, and millipedes.