We apologize but we have not heard of that happening and are not sure what would be causing it. We would recommend contacting the manufacturer directly as they make the units and would better be able to troubleshoot the device with you to get it working for your needs. You can reach Miracle Gro/Scotts at 888-270-3714.
When the Miracle-Gro Garden Feeder has used all of the chemical you poured in for the needs for your lawn the reservoir attached to the sprayer would be empty.
There should be no issue using Miracle-Gro Garden Feeder now when used as directed on the label.
No, there is no internal tube in the Miracle-Gro Garden Feeder. There is no need of one with this feeder, as the water gets fed into the feeder and then cycled back out through an internal syphon on the inside of the cap.
Miracle-Gro Garden Feeder comes ready to use and premeasured. The product in it cannot be removed and measured out for another sprayer.
The Miracle-Gro Garden Feeder is made to be used with water-soluble plant foods, which would be a solid granule concentrate. According to the manufacturer, a 1 lb packet of plant food should make approximately 40 gallons of solution to cover 400 square feet, and it would dispense in 10-12 minutes. The feeder will dispense 4 gallons of solution per minute (about 15 Liters). If you are having trouble using the sprayer you purchased, please contact the retailer from whom you purchased it, or you can reach Scott's directly at 888-270-3714.
The lock on the trigger of the Miracle-Gro Garden Feeder could be used in either position. Locked would hold the trigger down so you do not have to.