Maybe I didn't explain myself well............more fish, hence more food input = more ammonium, urea, waste and also a larger bacterial population to process everything. It's all tied together.
Here's another explanation that may help...... Two 100g tanks have the same exact P04 and N03 test results. One has starving corals, slow growth and poor coloration with a 3 fish population. The other has 8 fish and great color and growth. The through put of nutrients is much higher with 8 fish so there is more bacteria, nutrients, ect for the corals to consume.
The only other way to fix the 3 fish tank may be to reduce export, but it's much easier to add more fish and also more fun.
I just went through this with a friend of mine for the second time with him as he got back into acros after a few years.
Our test readouts were almost the same but he was feeding his fish every other day and small amounts of mysis.
I've seen this same scenario over and over again through the years. I've helped many people with this issue and it always goes into not enough nutrient throughput.
The big and only difference is that I know what I'm putting in my system. The bottle contents of a commercial bacterial products is unknown. It's also very easy for the companies to say anything and convince you with marketing psychobabble and claims of success.
You want to create a balance not continually rip everything from the system only to have to put it back in.