Fishing Nymphs in Stillwater

[happybob91]

These past two years I have really been into stillwater fly fishing, and have noticed that I often do well with nymphs. Even though this is going on, I still feel like I'm not sure I know exactly what I'm doing right. Usually when I fish the nymph I throw it out (with out any extra weight) on fast sinking line. Then I actually let it sit. It almost feels like glorified bait fishing. My question to everyone is how do you fish nymphs in stillwater. My 3 main questions are

1. Do you ever put action into your nymph and strip it in?
2. When would I know when I need to change the size?
3. Does the life span of a nymph differ in lakes compared to rivers?

Answers to these questions and any other info about nymph fishing in lakes would be great
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