So I did my first ICP test last year. I wasn't unhappy with how things were, but knew they could be better. I took it as proof I needed to change things. At the time the only things I was doing was WC with reef crystals, alkalinity (and sometimes some calc) from red sea, live phyto and red sea AB+.
I changed to aquaforest reef salt and started aquaforest Micro E. I was and still am scared of trace elements. Putting stuff in you can't test for at home is worrying. I did a slow transition to AF salt and started the trace element supplement very slowly. I'm still only at 75% of the rec dose.
I actually plan to do a follow-up test any week now. To see the changes in terms of numbers. But the tank is much happier. Gonis are thriving, pretty much everything is better. (Always going to be some outliers to just make your life difficult.)
Some of this depends how deep you wanna dive both in terms of money and time. I will say I am considering the Triton supplement where you send in a test every month and they make you a custom mix of elements every month. It's a bit pricey, but may be worth it. I need to see what my follow up test shows.