Miracle Grow Garden Feeder???

[VandaPanda]

Hey Folks,

I'm new to Orchid Board and posted about my other vanda and thank you for the replies that I recieved. Im curious to know about the Miracle Grow Garden Feeder. Its a feeder that you connect to your hose and distributes fertilizer while hosing my vandas. I (of course) emptied out the miracle grow fertilizer and just add 2 tablespoons of 20-20-20 and fill it with water. Im wondering if anybody else uses this device or knows about it.
It gives the measurements on the side: IE; (When starting with a jarful (1-1/4 pounds of Miracle-Gro) you will have 50 gallons of plant food. 1 jarful will cover 500 square feet of garden area or 1000 square feet of lawn. Recommended water pressure is 40 - 80 PSI. The feeder dispenses at 4 gallons per minute (1 gallon every 15 seconds).

I tried to do the math but I have no idea if this is good or bad for my orchids. I wanted to ask for some help so I dont get stuck in a bad routine. Also will I see any symptons if Im over feeding??? Thanks for any and all replies. Everyone on here seems cool and I appreciate it!