Hey brother I feel your pain! I've had similar issues with both frogspawn and Duncan. Frogspawn has had the same head for 6 years. Had a Duncan that grew about 10-15 heads while I owned it and then suddenly demised and could not for life of my figure out why. Let me share just some personal observations with my experiences with these corals:
I've always had fairly high lighting and definitely lots of flow. My system has also been ULN for around 4-5 years now.
For the first year of having my frogspawn I kept in highlighting near top of the rocks. I can tell you firsthand that in my setup it did NOT seem to like this. I know have him at the bottom of the tank under a gen 1 Radion running at 58 percent on coral lab LPS mode. Seems to like the lighting.
I can tell you this: the time in my tanks history that I noticed a DRASTIC improvement in the size, growth, and health of this coral and the Duncan seemed to happen during a year where life was really hectic for my wife and I. I spent very very little time maintaining my tank. In fact I dare say the only maintenance I did on my system for the better part of 4-5 months was top of evaporation with rodi water and feed fish every couple of days or so. No water changes, additives. Nothing. I did run my refugium with miracle mud and chaeto.
I remember when I finally did get around to paying attention to my tank again, I noticed my frogspawn was HUGE! It had nearly doubled size and grown two additional heads in that time that I ignored my tank. I remember I got excited and that spurred me on to get back to regular maintenance. Well over time it started to wilt again until now and it is back down to a single head about the size of a golf ball. Now I'm not saying all this to tell you to quit doing maintenance. These are just my personal observations. I am now in a protocol of heavy feeding, dosing nitrates and bi weekly water changes (to replenish minerals) and it seems to be growing again. I'll continue this until my tanks inhaditants show me otherwise as I'm convinced that in this day and age with all of our ulns, biopellets, carbon dosing and skimmers the size of silos that we are creating some anorexic reef systems. I've decided to go back to a little bit of a dirtier system and see what happens as I can tell you this ulns thing has NOT served me well in my six years of having this system up. My corals have great color and health it seems, but growth has just been pathetic at best and nonexistent at worst. These are just my experiences and I know there are many successful reefers on here that run beautiful and successful ulns reefs, but I think those goals are better suited for sps reefs which seems to be the current mass obsession for about 90 percent of hobbyists today. I'm looking to get a tank full of soft, LPS coral and zoanthids personally so we'll see how it goes.
Also I would say really pay attention to stability. You mentioned your salinity ranging from 1.022-1.026. This is a VERY large range. Salinity needs to remain as constant as at all possible. Mine stays at 1.026 on the money, all the time.
Hope this helps a bit
