Just to add some to what people are already saying. In my experience with Cyano it's really a nitrate problem. I don't think you are getting these problems because of too much fertalizer. I would load that tank up with nitrates, phosphates and micro nutrients. You really need to work on getting good plant growth. The fact that your plants aren't growing well tells you that you're missing something.
Many of us have had the same story and it really takes a lot of time to get things right. If i were you I would try to lower my lighting a bit more dose with ferts and water change once a week or so. I have been able to grow an HC carpet very easily with low light. In fact anytime i tried high light it would die pretty quickly and look terrible. This was even with CO2. HC is a bit of a CO2 hog so to allow the plant to gather enough co2 you should limit the light so that this becomes the limiting factor. Excel does work great with HC in my experience it loves the stuff so i would keep dosing that to help stimulate growth.
Lastly, Patients is a big issue too. Once you make a change you need to wait a while almost a month to see if it works. Your tank is reflecting conditions or about a month ago. So even if you have everything perfect today but things were screwed up a couple weeks ago it'll take time for you plants to get used to you new conditions. Algae is much better at adapting to new changes and plants are terrible at it. The only way plants can beat algae is if they have optimal condition's day in and day out.
Again i just want to stress that it really takes time. I struggled for about 2 years before i got it right. And its still a battle. It is very rewarding once your plants are growing really well.
I think your tank has the potential to look really amazing. I would not use the Abx and just try to fix the problem first. Good luck.