The issue with Excel is that once you use it, it alters your water chemistry by adding that co2. Either you keep up with it and dose it daily/every other day or you don't dose at all. If you only dose every now and then you are altering your water chemistry and making it less stable.
CO2 overdose causes a severe drop in O2 (this is seen naturally occuring in catfish farmers when at night, the plants in the pond no longer produce O2, the CO2 ends up suffocating the catfish and by morning every single fish is belly up.) the way to combat that is to use more aeration, catfish farmers use paddle devices to stir up the water at night so they always have enough O2. This isn't seen as much in the aquaria because, yes it does take a lot of CO2 to do that but at the same time, it depends on your pH level. If you have a lower pH level, you are more at risk of killing your fish with a CO2 overdose.
Anyway, I agree SAE's are good for hairalgae, my Golden Dwarf Barbs have been making a short job of it in my tank as well :)
Rembrandt II, Suiché
Leopards: 1:4 Hawkeye, Luna, Astrael, Dorian, Cullen
Gargoyle: Cloudjumper and Toothless