From what I understand the TDS meters only measure conductivity and can't account for things like tannins, but admittedly I'm not sure what the ideal range for these guys would be. I've always assumed as low as possible is ideal but I've got more to learn. You are playing on the safe side and I think that is the proper course.
I thinkCharney has some panda who ended up pairing up and killed conspecifics, I'd be worried that the amphs will not be excluded from any similar aggression.
Absolutely trying to stay on the safe side. They cost too much to take any risks lol. I'm sure the amphs would be toast if the pandas paired up. I'm going to keep a close eye on aggression levels for sure. Honestly, if I ended up with a breeding pair of pandas I would have no problem moving the amphs around to accommodate the pair.