The problem with spirogyra is that you can have a prolific amount of it, but the root cause was temporary and simply a trigger regardless of how balanced your tank is currently. I had an outbreak I fought for a long time that started from am ammonia spike related to adding a handful of Amazonia to a relatively established tank, and with Tom's recommendation tried AlgaeFix. It worked beautifully and has not come back since.
I did remove my inverts, however, but saw no ill effects on my fish or plants after following the directions.
Thanks for sharing your experience. I guess in the future I could try to remove my inverts. Finding and catching them all seems like it would be a huge PITA, but I guess maybe not as big a pain as doing what I did.
Tom, thanks again for your response. I don't exactly know what my trigger might have been, but I'm sure overly dense plant growth leading to inadequate circulation, intense lighting, etc. played a role in exacerbating the problem. I'm fertilizing using EI method. While cleaning the tank, I did find 2 dead assassin snails. Idk if that would be enough of an ammonia spike to trigger the outbreak.