Hey, many just use the Advanced nute calculator for their GH 3 part as well. I read this long article that took place over a couple hundred grows and showed that the 3 parts both had like 99% of the same properties and what not.
Also, keeping your res under 70D is a good/great idea to avoid root rot issues. I will be honest though, I rarely check mine, but an aquarium thermometer is only a few bucks at Walli Mart.
Adieu
