Not entirely true. "Chemicals" is a very broad term. A lot of chemicals are harmful and certain mixtures crash the tank. Don't chase the numbers isn't a "catchy" phrase either. Plenty of people who have dirtier waters and manage to have great tanks, whereas others their tanks go completely downhill with those values. Numbers usually indicate what could be a problem, but it doesn't mean that it will always work for you the best, for whatever reason that may be.My main issue is the 'chemicals are bad' ideaology. What do you think food, water, fish, corals, etc. are made of? It is a ridiculous statement that I see on here often (and in many industries) made by those who have no understanding of the basic chemistry of the world, or simply don't want to learn. It is a foolish notion with no sound reasoning behind it.
Also, numbers are fine to target. The saying "don't chase numbers" is just a catchy phrase that is used when someone doesn't understand why a test value should be in a particular range, or when someone wants to justify their laziness. It is an irrisponsible statement that always annoys me when I see it. No one is saying you can't have variations in a test value, or that you need an exact value for each parameter. You just want things in a certain range, not just for the known issues that arise when the values are very far off from optimal, but that, in order to tell what is wrong with a tank (be that algae, fish, coral health, etc.) we need to standardize the common parameters of a tank. If not, no one can help you as you would be introducing too many variable if you just say "I don't test because targeting certain values is bad." In order to diagnose a problem, you need to eliminate variables that could be a cause of an issue. When everything is within the right range, you can assume with a fair amount of confidence that the issue at hand is not from a value drifting outside of a healthy range.