How long has your tank been set up? These sound like normal startup issues.
Flourish and Flourish Excel are basically the same thing with Excel having the addition of carbon (liquid CO2), the micronutrient mix is almost identical.
Incorrect. Look at the label. Excel is completely different from Flourish Comprehensive.
I think you mean Flourish Comprehensive and Flourish Trace are almost the same thing. These products are practically identical except that Comprehensive has a very small amount of NO3 and PO4. Excel is glutaraldehyde. I don't think there are any micros added to Excel.
As long as it is not overdosed, Excel actually reduces algae rather than helping it grow. That is why people spot dose their plants to kill small patches of algae.
SeaChem has a confusing product line. Flourish is the family name and Excel/Comprehensive/Trace/Iron/Phosphorus/Potassium/etc. are the products. They made it more confusing by making the family name and the product the same for Flourish (Comp/Trace)
The root tabs are being dissolved by the water flow through the UGF and taking those nutrients which would normally be bound in the substrate and blasting them around the water column. Because you have all these nutrients floating around and not enough plants (and CO2) available the algae is going to continue to grow.
Swords, crypts, vals are very common plants that are notorious root feeders. Floating plants, or plants that do well attached to something are water column feeders. (Java ferns, Anubias, mosses, elodea, hornwort, etc.) This is a VERY generic and simplistic explanation. Look up the types of plants you want or have and then go from there.
If you want you can keep one half of the UGF and have that half of the tank with the water column feeders and the non-UGF side use root tabs and root-feeders (Swords). (remove the unused plate if possible)