maybe my skim reading skills are faltering. skim...no pun intended of course.
Did anyone ask about the actual phosphate and nitrate readings?
I would 1st start there to find out where the tank parameters are exactly at.
Are your bulbs cooked?
Is there direct sunlight hitting the tank anywhere?
Are you adding a wee bit too much iodine as well?
Bioload. How many fish/snails/crabs are in it?
What kind of coral food are you adding and how much and how often? Are there before food addition and after nitrate and phosphate readings being taken just to see if there are big nutrient level jumps?
Why do I pose these questions and ignore the skimmer? Start at the input end of the equation before you start out at the output end. If it works out you're too high on the input end then maybe you need a 300 to 500 gallon capacity skimmer or change your input practices and or bioload. And then again a simple GFO and carbon monthly or bi-weekly use with the water changes already in practice might just dial it all in. Or maybe just make sure that your snail population is where it needs to be(clean-up crew). My one 90 has well over 60 small hermits and 80 or so snails. Without it I was having algae issues even with water parameters where they needed to be.
Back on the input or bioload side of things.
A 150 can hold alot of livestock. And alot of livestock produces lots of waste especially if being overfed or pushed with foods and additives to make it all grow super. Which when I setup 1st 90, way back when, after moving from lil 55 I was doing myself until I started to learn the moderation practices required. Kinda like the overwatered plant syndrome or killing it with kindness.
What's going in? How much is there? What are the nutrient readings.? Then you can establish the problem and then target the best step. Most will say and I can agree, You can never have enough skimming, but maybe you're overlooking other problems just as easy to solve.