Not sure if loaches are appropriate for dealing with algae in the manner that you have described. As for issues with loaches' barbels with EcoComplete, I've read that it is fine though sand is almost always preferred.
I have a Planted tank and switched from using a combo of Seachem Flourish Comprehensive + API Leaf Zone to Green Leaf Aquariums' PPS-Pro System (its a set of dry fertilizers you mix with water). Its is dosed daily and is quite economical. I occasionally use Seachem Excel for spot treating black beard algae. It is a "carbon source" for plants (though that may be up in the air) and it will not make an algae situation worse. I started off with DIY yeast based CO2
and then moved on to a pressurized setup.
As for the algae on the glass below the substrate line, use an old credit card to scrape it off.