You in hydro? 6.6 is a high pH for that, that's what you would want in a soilless setup. And judging EC on an organic often fails- the organic nutrients don't register the same as chemmy ones on your EC meter.
I'd only use fish emulsion and similar organic goos if you are familiar with organic techniques, especially in hydro- the chance of gumming up your system is much higher. As a soil fert, I've given it in veg as a N supplement when my plants look N deficient and I'm certain it's not a pH problem or something else. It also works to turn a bloom fert into a veg fert in a pinch- your average bloom fert is fine in veg too, if you use it at 1/2-2/3 strength and supplement it with fish emulsion. But again, you should be familiar with growing and diagnosing sick looking plants.
I guess fish emulsion is one of those things, lol. It's great stuff; use it with care by the 'less is more' philosophy, and it is hard to screw up. If your leaves look dark, dull, and droopy, stop and flush- you've given too much N.