Kay, I don't 'do' hydro typically but I have hear of people even using molasses in the res without issue. I personally used TopMax in my flood-and-drain without issue.
I don't know about fish emulsion. I DO know that it tends not to stay suspended in the water very well so if you find that hydro growers are using it I suspect you have to have a res that is being mixed all the time.
Um... yeah... definitely post this as a new thread in hydro!
As for low temps, yeah your yield is likely to suffer... ALSO have you considered a cold res as a possible source of your deficiency problems? Just a heads up that you can't really play around too much with forcing the purple using cold temps unless you have good control over your reservoir temperature... nutrient uptake changes at extreme low and high temps and you are very likely to see problems.
Again, I'm not a hydro person; hydroponics is the Dark Side and the closet I'll get to crossing that line is drip-to-waste coco, lol!