Let’s start by wrapping your code so we can see it better 
Watch the animated gif at [README] Welcome to Blynk Community!
Then, I believe you should be using the variable pinValue instead if i to output the slider value to the Value Display.
As for further code usages, I recommend https://www.arduino.cc/en/Reference/HomePage combined with trial, error, trial, error, trial, success… works for me 