Obviously the people commenting here know what they are talking about and you should follow the tactical advice given.
My advice is more strategic. Like others have suggested, your tank is really young and it just takes time. I would focus on getting montipora to grow first since they are one of the easiest and most forgiving. You could also try pocillopora to start with. It sounds like you're on top of your maintenance so you're probably better off not worrying about it too much and enjoying your tank. It's a long process and you'll get there.
I would also put the Acros on hold temporarily and save yourself the expense and frustration. I have both Hydra 26s and Hydra 52s and, based on my experience and observation, I think it will be a challenge to get anything but the most robust Acros to grow under 26s. To put it into perspective, my tank has similar height and length dimensions as yours and I have 3 Hydra 52s. I still get shading and have not been able to keep the more challenging, light-hungry Acros. That being said, you don't have to have a tank full of exotic Acros for it to be awesome. I know that's not something you want to hear since you just bought those lights less than a year ago. Probably isn't even true, just my personal (i.e. worthless) opinion having used AI lights over the last 5-6 years.
If you're interested, I'm happy to help out. I know how frustrating it can be to watch frags you spent your hard-earned money on inexplicably die off. I have several different montiporas that have been rock solid in my tank over the years. I'll break you off a couple frags for free if you want to try them. I also have a PAR meter you can use. I think you'll find the 26s are not as powerful as you think they are.