Here’s an interesting question. What’s more important? The split shot or the nymph? If you cannot get the nymph to the proper depth, the fish will ignore it. Therefore, selecting the right amount of split shot and positioning it correctly on the leader is more important than the actual fly! Now, as soon as I state that opinion, I also need to recommend it’s best if you can avoid using split shot at all – no need for extra hardware banging around.
To keep from using split shot, pick a fly with enough weight to get down to the bottom. However, in a fast current, that may result in a huge, unrealistic fly bouncing along. As a new fly angler, it is crucial to understand that the current must move the fly naturally. To solve the problem, use a tandem rig with the weighted nymph as the first fly (basically duplicating the function of the split shot) and the light fly as the trailer. Most anglers tie the trail fly off of the hook bend of the lead fly, and this puts tension on the lead and reduces its natural movement. To address this, more anglers are tying their tandem rigs using a tag dropper since it allows both flies to operate independently without the lead fly being impacted by the trailer or vice versa.
Back to split shot. The first rule of using split shot is it is better to use a more massive, heavier shot than multiple small ones since a single shot is more comfortable to cast. One way to keep the size smaller (and reduce the corresponding splash) is to use tungsten shot instead of lead. Tungsten packs more weight into a smaller form factor with the added advantage of being better for the environment. An alternative to traditional split shot is putty. Putty comes in a blob, and you pinch off what you need. After massaging it to warm it up, form it onto the leader in a football shape, and it should stick to that spot while also allowing up and down adjustment. Unlike split shot, putty is reusable until it loses the ability to adhere to the line.
For fly fishing, split shot comes in sizes ranging from nine, the smallest at 0.05 grams, to ridiculously huge weights. The “BB” size being the largest practicable one for most fly fishing. Frankly, if you need more than the “BB” size, consider using a sink tip. If you buy a pre-loaded split shot dispenser, it will contain the most popular sizes. Frankly, I find the teeny tiny sizes eight and nine to be unusable, but that’s just me as a result of my aging eyeballs and fat fingers. Unlike putty, split shot clamps onto the leader and is not inherently sticky. When attaching, avoid squeezing with tremendous force since that crushes and weakens the leader. And, since you cannot just mash the heck out of it, it will slip.
There are different ways to prevent split shot from sliding on the line. The worst solution is to tie a blocking knot below the split shot because knots weaken the line. Since the fly fishing leader isn’t very strong, to begin with, the induced weakness could be the difference between catching and losing a beautiful fish. A better method is to wrap the leader back through the split shot. This puts a loop around the shot, providing more surface area for the split shot to grab on.
Another option is to tie a snell directly to the leader. Once tightened, the snell blocks the shot from moving. Tying the snell is simple – grab another section of tippet and make a loop and wrap the tag end through it as many times as needed for grip and tighten.
Put the split shot above the snell. You can quickly move both to adjust the shot to the right depth.
Another increasingly popular option is to avoid putting split shot on the leader at all. Instead, attach the split shot to a tag hanging off the leader. This allows the fly to move more naturally with the split shot hanging independently on the tag. To keep the split shot from sliding off the tag, tie a knot at the end.
Final question – how much weight do you really need? The rule of thumb is the distance between the indicator and the fly should be 1.5 times the depth. Obviously, you must play a bit to figure out where the fish want to see the nymph – especially since trout like to look up at their food. Be prepared to add or remove weight to achieve the right balance.