installed my ispring tank valve but it's leaking at the threads, i used teflon tape, what did i miss?

You didn't use enough Teflon tape, or you wrapped it backwards. The seal is insufficient.

1. Shut off the water supply to the system.
2. Unscrew the tank valve.
3. Clean the tank's metal threads.
4. Apply new Teflon tape. Wrap it clockwise (looking from above) around the threads 8 to 10 times. Do not skimp.
5. Screw the tank valve back on clockwise and tighten by hand. Do not overtighten with a tool.

IF THAT DIDN'T WORK: If it still leaks with proper tape application, the valve itself may be defective. Contact iSpring Customer Support for an immediate replacement.