Hey, depending on the super soil used, most are packed for 4-8 weeks of food inside of them for your plants. After about 7 weeks, I'd imagine that super soil was pretty depleted. Top dressing with more amendments, or switching to liquid nutrients to supplement them is needed and if what you are doing is clearing it up then you are on the right path.
With a super-soil, you've got a lot more things dissolved in the soil than just nutrients, a lot of non-plant food ingredients are in there as well. EC/PPM for organic grows as far as run off are a bit harder to do since the meters read the non-plant food ingredients as well.