Maybe chemical was used in a broader sense. Lanthanum chloride would be one example where as the juice may not be worth the squeeze.
Yes, it works. Great in fact. Cheap. Easy to administer. So far great. However if an accident happened it could very well be catastrophic. There are some reports by hobbyist of issues with some Zebrasoma tangs. Needs to be administered carefully or thought out at least to help to filter the particles (not sure right term here, sorry).
I've used phosphate rx with good results but I wasn't a fan of the residue particles. Dosing at night seems to help as did dripping it into a filter sock in front of the skimmer intake. Even with a filter pad in the sump it made it into the display. Did that harm anything? I have no idea. Polyps are out at night so part of me things they ingested it the other part of me says no, they don't. They know what is and is not food. Then I just shrug and say I'm not a marine biologist and leave it at that.
TL; DR - LC would be an example of a chemical. At least that I think of.
Edit: hope your morning is going well.