Well I did some reading on the forum and some say take away nitrates and some say add. Some say add phosphates and some say take away.
I'm confused. I hope my tank looks better tonight when I come home.
I am by no means an expert on aquarium plants and algae, and all I can share with you is what I have seen first hand. Although not new and many hobbyists and gurus have been saying this, I have seen algae begin taking root when plants start doing/growing poorly. It is almost a given as I have now seen it in more than one tank. The reason that the plants do poorly is usually due to some nutrient deficiency. If you have a low tech tank, overtime nutrients in the water column may become depleted and fish waste may not always be enough to compensate. Even the substrate will eventually become devoid of nutrients. This creates an environment friendly to the growth of many types of algae. If you have a low tech tank, you may still need to dose in very minute quantities, some ferts in order to prevent plant deficiency issues and the possiblity of a hostile algae takeover of your tank. I would suggest doing water changes two times a week for a while to get rid of some of the excess organics that may be feeding the algae, dosing some nitrates, potassium, phosphates, and a trace element fertilizer like Seachem Fluorish Comprehensive with every water change. You only need do this once or twice a week. I would also suggest that you cut down your lighting period, and continue with excel at twice the dose with every water change. Also, try and add some floating plants, like cardamine or egera densa, temporarily. I have seen on more than one occasion where I had tried everything and lost hope that the algae would ever go away and then miraculously after adding floating plants, the algae seemed to quickly recede after 2-3 weeks of adding the floating plans. Hang in there and do these things and eventually, your tank will snap out of it and regain its pristine lustre.
Also, did any fish die lately and are all your fish accounted for. Sometimes a un-noticed fish death will cause a major ammonia spike which in turn could give rise to a major algae bloom.
I really don't believe that the Excel caused the algae bloom. If anything, it was probably a coincidence, nothing more and nothing else.