Well how did they go to 470 from 120 in one week? Weren't you checking things and diluting back to make sure the number didin't get too high?

some of that number might be dust from your hydroton but there's no way to know for sure.

I'd dump that stuff and start over. And you shouldn't let your ppms rise that much between water changes.

You should keep your ph between 5.6-6.2 if you aren't already and check it several times a day.....again if you don't already.

Good luck.