PAR output is affected by all sorts of things. Adding carbon will increase your par since the water will be more clear. PAR will drop over the course of a few weeks after installing new T5HO bulbs. Even changes in circulation, the turbulance on the surface, affects PAR. The type of lighting makes a difference, too. Point source LEDs like a kessil mean you can get 250 PAR when the sensor is facing towards the light and 80 PAR when it's facing 90 degrees from the light.
Also, PAR isn't the be-all-end-all. Chlorphyll photosynthesizes best at certain wave lengths:
https://www.khanacademy.org/science/...hetic-pigments
A very blue light at 200 PAR might be blasting your corals compared to a white light at 200 PAR.
There are also species (typically deep water) which don't like red spectrum light. Here's one study corellating red light with poor coral health:
https://pubmed.ncbi.nlm.nih.gov/24658108/
Deep water acros were best under blue spectrum, grew at half the speed with the same par but half blue and half red, and died under red. Shallow water acros grew at the same speed with either blue or blue/red, but also died under just red.