CONS
Now, there are some cons to using split shots. For example, you can easily tangle up your line while casting. On a more environmental focus, lead split shots are toxic to freshwater ecosystems. You can easily use tungsten and tin split shots. While choosing between using heavily weighted nymphs or split spots, it is equally important to know when to add or reduce the weight.More Weight?
If your nymphs are moving by too fast, add more weight. This means your flies aren’t getting down fast enough and are getting caught in the quicker currents. Either add a split shot or tie a heavier nymph on.Less Weight?
If your flies are hanging up (getting caught on the bottom/snagged) too much, there is too much weight. Either switch the flies out or remove a split shot.Remember, flexibility to change is extremely important. Both Joe Humphreys and George Daniel strongly support this principle.
When casting a lighter rig, you're going to want to cast far enough upstream to allow your flies time to get to the bottom. The distance will change based on the water depth and speed. No one, not even me, can accurately tell you the exact distance needed. Just use your best judgement.