When you say your water is of excellent quality, what do you mean? Any idea on GH and KH at least?
Otherwise:
- First up your dosing to the 100-125gals
- Stop dosing excel, especially double dosing!!! it only kills plants and fish when overdosed. This is really something toxic if not dosed as recommended. Excel in a 100gal is just a waste of time/money, just adding on CO2 fluctuations as it doesn't live long in tank
- No need for all those blackouts, you only make your plants weaker and weaker, let them grow, only prune/trim/retop if needed
- Make 2-3x/week a 70-80% WC for some weeks until algae is away, this is the key for algae, overdose EI after each WC to compensate
- Putting the luminaire higher is normal to see plants stop pearling, they need to adapt, but they will do if you let them take the time, just wait and see, you can't loose anything since they're dieing anyway, right?
- Rising it high is not a waste of money, it's just a temporary adaptation to make your plants survive algae, once done, after MANY weeks, you can lower it again slowly and even add some burst periods with the other 2 bulbs
My advice is to not hurry, to let plants adapt, they need 3-6 weeks, even more sometimes in my expierience. While they adapt, 2-3x/week WC will control algae
Follow this, don't change anything for some weeks, except focusing on CO2 to make it STABLE. Plants can't adapt if everything fluctuates/changes (light, ferts, CO2...) every 2-3 weeks like now, they need stability.
I'm sure your tank will grow and algae regress. Also, you can manually remove those algae as much as you can between WC.
I well know what you're living, here's my tank how it was:
Then, how it looked, no blackouts, most are same plants!!!
Read also this topic:
http://www.barrreport.com/showthread.php/5665-Lighting-directions-outdated
Will make you wonder about light, just like made me stop using my 4x54W T5 on my 60gal and hanging my luminaire higher, it works as you see
Good luck