IMO algae in saltwater is much harder to manage than in a freshwater tank.
Maybe it's because my saltwater tank is only 21 gallons and I have no room to keep a tang long term, but you not only have to worry about nutrients getting to high, but also too low in saltwater when it comes to getting algae issues.
The only algae problems I get in my freshwater tank is on the glass, on the gravel, and a small amount of algae that kinda looks like moss grows on my java moss, but none on my rocks and driftwood (although possible your added CO2 and higher nutrients played a role in that). My only CUC are those snails which hitchhike on live plants.
However, everyone I recognise how everyone has different experiences and I've never attempted to set up a high tech planted tank and never tried to set up an SPS reef, I just know the many challenges of setting up what would be considered a "simple" reef tank (soft corals only), plus there's a lot more to learn when first starting out for reef tanks.
Also for freshwater clean up crew, have you considered bristlenose catfish or plecos?
It's been a while since I've done any research on freshwater fish, but I don't remember hearing anything about those fish having a risk of eating plants.