Has anyone heard of or tried Trilon M as a chelator? The chemical name is methylglycinediacetic acid (MGDA)*. Apparently, Trilon M was the first product to meet the US EPA’s Design for Environment criteria for chelating and sequestering agents (in 2011). There’s an old press release about it
here, and links for technical info and msds are provided at a supplier site called Saveoncitric. It’s pricey for a 10 lb bag.
https://www.saveoncitric.com/trmpo10lb.html According to what I read, it works well at high pH, has low toxicity to aquatic organisms and is biodegradable.