I just started using algae fix for the first time as I have this string algae that is seems to love the same conditions as the plants so it only struggles when my plants struggle. So far it isn't working well for this type of algae, but did get rid of the small amount I had on the glass and driftwood so I know it's doing something.
However, to my surprise, my plants didn't even flinch. I knew it was plant safe but I thought it would have some effect. They are just growing as they used to, still getting great growth and color, so not seeing any side effects there. Snails are dying but that's fine by me. Fish is not acting/looking any different.
Just saying, I had my concerns as well and now I am confident that this stuff is safe for plants and fish.