Whoa... talk about bring a thread back to life!
I figure if you could afford an autodosing perstaltic pump, you could probably go the extra $65 and avoid the risk....
As for trouble, are you worried about over dosing the 65 or under dosing the 90? I guess under dosing would be better than over dosing if you fertilize from the same line.
"What we do in life, echoes in eternity." - Gladiator
If I could harness the power of the sun, I'd focus it on my plants and watch them grow.