For myself, I have been using flouro almost exclusively for the past year or so, regardless of whether I'm fishing dries or wets. I know that this probably flies in the face of convention for some, but it's what's been working on the waters I've been fishing. And those waters tend towards shallow, super clear, and slow moving.
Fact: Flourocarbon line is denser than water.
Fact: flourocarbon line is not as dense as tungsten impregnated line; it will not sink like it. It sinks verrrrry slowly.
I started using flouro for dries while fishing a small gin clear creek last year, pretty much by accident. See, mono floats, and on bright days the light would refract through my mono as it floated on the surface, producing several 'balls' of shadows and flares that moved accross the bottom, spooking every fish in a pool.
Well, one spring day I was hiking up the creek and saw a two foot brown feeding in a pool. I had seen this submarine before, but had always spooked him on my first cast. This time I had been fishing a nymph rig and had a couple feet of flouro tippet on the line. I saw him taking some kind of caddisfly off the top, and without thinking I cut my nymph off and tied on an elk hair caddis. I flipped this offering out to him and realized as it touched down that I had flouro on. Well, I thought, there's a wasted cast.
I figured it would sink the fly in short order, but was surprised to see it float down towards the feeding brown. The flouro sank quickly, to about an inch below the surface, and lo and behold, no flares and shadows. The fish came up and slurped my fly. I wish I could tell you that I landed that beast, but almost as soon as I set the hook, he plunged for deeper water and snapped me off.
However, I found a 'new' trick to put in my bag. For the next several trips I experimented with different brands of flouro (I like Berkeley's professional 100% flouro, but I would say that any good quality flouro will do the trick), as well as with line diameter (I use 4 lb. mostly). What I have observed during my experiments, is that light flouro will not sink a small dry as long as it's relatively short (I tend to like about two feet) and the fly is 'modified' with a little floatant. It sinks just below the surface, making a very shallow bow, which becomes essentially invisible to the fish. Now, some people have told me that flouro will sink the fly after a few seconds. In fact, I've timed how long the fly will stay above the surface. I tossed a # 18 para BWO with three feet of 4 lb. flouro as a tippet into a pool and waited over 2 minutes before getting bored and picking it up. In other words, don't worry about the fly sinking if you use some common sense.
I found that I can use 4 lb. flouro with dry flies, as long as I apply floatant to the fly and grease the leader, not the tippet. Also, I try to keep my tippet length under three feet. Of course, I also take into account whether the fly is made of closed cell foam, or just hackle, the speed of the current I'm fishing, the size of the fly, etc. But, if I'm fishing between 9 to 11 foot leader/tippet combos, this general rule has served me very well over the last year. I think that if you do a little experimenting of your own, you'll find plenty of times to use flouro with dry flies. And plenty of times when mono will do the job at hand better.
"Three-fourths of the Earth's surface is water, and one-fourth is land. It is quite clear that the good Lord intended us to spend triple the amount of time fishing as taking care of the lawn." ~Chuck Clark
I only use fluoro tippet for dries in 6x and smaller.....my leaders are always mono - and for bigger size tippet I stick with mono to keep the fly afloat I find however with 6x or smaller I'm fine even when fishing small flies - and Iu do want the tippet attached to the fly to be submerged, etc I sometimes also use snake river mud (by loon) to take the sheen off the last 2 feet and help keep it submerged) If I were only nymphing fluoro all the way
Fluorocarbon when treated with floatant will NOT sink. In fact, nylon's specific gravity is higher than water so it floats because of surface tension and because it is lighter than water.
Most nylon mono has a specific gravity between 1.1 and 1.2 compared to fluorocarbon at about 1.8. So fluorocarbon is 50% denser than nylon mono. One might think that this would cause the fluoro to sink but what it does is that it causes the fluorocarbon to indent the meniscus more.
Since the depression of the meniscus increases the visibility of the floating line and it increases the refraction of light onto the river bottom, it makes the line more visible.
However, when fluorocarbon is sunk, it becomesless visible that nylon. The best leader material for floating flies in thin clear water is not floating mono but sunken fluorocarbon. If fluorocarbon is unsuitable, it is not because it sinks but because it is more visible when floating.
The best tippet material is for spooky fish is actually tippet that has been treated to remove the oily coating and sheen from manufacturing and been treated to sink just below the surface. Degreasers and sinkants are sold just for this purpose such as Loon Snake River Mud or "tippet degreaser" such as Airflow Tippet Degreaser.
"Being slightly heavier than water does not mean that nylon monofilament is going to sink, at least not quickly or very well. Surface tension—where the water’s surface behaves like an elastic film—must be broken before an object will sink. A object’s density and contact angle with the water’s surface are the two most significant variables in its ability to break surface tension and sink, and the “just slightly heavier than water” specific gravity and zero contact angle (i.e., laid out flat) of a nylon monofilament leader or tippet are not sufficient to do it most of the time. If pushed or pulled under the surface by a weighted fly or roiling current, nylon monofilament will sink . . . but very, very slowly.
Fluorocarbon has a specific gravity in the range of 1.75 to 1.90. Tungsten it ain’t, but it is significantly more dense than nylon. But is it sufficiently dense to quickly and reliable break surface tension and sink all by itself, even at zero contact angles, and even in the smallest diameters? No, it’s not. Our testing reveals that most brands of fluorocarbon tippet material in 0X to 8X diameters are no better than nylon at breaking surface tension and sinking on their own. Larger diameter fluorocarbon materials do demonstrate a slightly better ability to break surface tension without the assistance of current or other external influences, but for practical fishing purposes fluorocarbon has little benefit over nylon on this measure."
Silver I find your opinion interesting but some what in error (likely a typo) as you indicated that, "In fact, nylon's specific gravity is higher than water so it floats because of surface tension and because it is lighter than water. " It floats because of surface tension but is heavier than water and lighter per unit than is FC. Water has a density of 1 while Mono skids in at 1.1 or so while FC rate a higher 1.7 mol.
You went on, "Since the depression of the meniscus increases the visibility of the floating line and it increases the refraction of light onto the river bottom, it makes the line more visible." I disagree there also as the meniscus or curvature (curved depression) caused by the tippet floating on the surface film due to surface tension, becomes sharper with FC as it is thinner and more dense and therefore heavier per diameter so we agree somewhat there but it seems to me that this then allows less of the FC line to stick up above the surface catching the light and refracting it into the water. Additionallly the meniscus will have a sharper and deeper curve therefore a much narrower surface print, again aiding invisibility. Add to that the reflective index of the FC and it wins the invisibility contest above or below.
Another factor that hasn't been brought up is that for equal strength FC and Mono the FC will be smaller diameter and remain so as it doesn't soak up water as does Mono which increases it's diameter. With that soaking Mono loses strength while FC does not which is yet another factor.
Of course you pay for all these benefits hence the much higher cost of FC leader material.
Like I said above the proof was in using it and finding it much easier to sink while keeping just a tad of the tippet floating with conditioner in front of the fly thereby not spooking leader shy fish.