I am using Fox Farm trio at 1/4 strength.I was under the impression that Cal-mag was needed if you're using distilled or RO water?
Cal-Mag reps love to hear this phrase, they've done a great job selling it to cannabis growers.
I have no idea what the calcium and mag levels are in 1/4 strength fox farms trio. I run close to 8:16 of GH micro and bloom. I would suggest hitting
angelfire and looking for their nutrient calculator. Plug in the values of your nutrient, see how close they come to the lucas mix. The lucas mix is not perfect, it's probably the best 'generic' mix information available I'm aware of.
The balance for cannabis is approximately
N 130
P 106
K 183
Mg 73
Ca 130 (this is what the lucas mix provides. Not sure if this is what your strain desires)
S 49
The closer you can get your nutrient profile to these numbers, the fewer nutrient related issues you'll have. You'll be able to feed higher levels of nutrient without burning or overfeeding and you'll be able to run a reservoir longer without creating excesses of any element. Those numbers are not perfect and the mag needs change by strain/phenotype. I use magnesium sulfate for mag application by strain.
Edit: Oh... the calculator there is only for GH nutes. Bleah. You'll have to look at the values on the back of your nutrient bottles and do some math... my apologies.