Substituting Hypo with Ammonium thiosulfate?

Hello,
I've been wanting to develop ECN-2 from raw chemicals. Ammonium thiosulfate is quite hard to source here in small amounts, so I've been wanting to substitute it with Hypo. I know C41 & ECN-2 fixer (which uses Ammonium thio) works on B&W, but I'm wondering if it will work in reverse because of the thiosulfate ion. Will I just have to change the fixing time? Or will the pH be affected?

Welcome to Photrio!

Modern Kodak color negative films (including Vision 3) are at least in part based on T-grain technology. This means they'll fix out very, very slowly in a plain sodium thiosulfate fixer. You could try adding a bunch of ammonium chloride etc. to try and make a quasi-rapid fixer; this might work OK, esp. on the higher temperatures of a color negative process. However, I'd recommend trying to get some C41 fixer instead, which will be guaranteed to work.