I like to try out the advice i'm given before i pass it on. just to be sure that i'm not spreading misinformation.
That would be ideal. Unfortunately it's not possible to take the time to test every bit of knowledge that one has. Do you really know what will happen to you if you jump off a high cliff? Most of the things we know, we know only because we trust the sources that told us. I've never measured the circumference of the earth, but I am very confident it is what the astronomers say it is.
In this case, I have heard this said about Fox Farm from several experienced growers over a period of time. I felt it was reliable enough to follow and repeat.
Perhaps you would have preferred that I had prefaced that statement with "I have heard that...". I probably should have, but criminy, discussion in this forum is very relaxed and informal and people don't usually take the time to state all the qualifications that apply to a statement. Are we really that cagey that we say things like, "I read in wikipedia that some astronomers believe the circumference of the earth at the equator is about 25,000 miles?"