Apple juice and similar typically attracts fruit flies, not fungus gnats. A bit of dish soap in the solution insures that they sink to the bottom. Are you certain that these are fungus gnats?

I've had the same issue and for long enough that I've gotten really good at catching them with my bare hands & also tried apple cider vinegar traps, which weren't that effective. There are suggestions out there of using plain soap water traps or lemon scented soap water with vinegar... so you can try variations on your traps. Problem is if these are fungus gnats, they won't care so much for the traps & will stick to the plants - you'll end up catching only the ones that venture far from the plants, which is a small fraction.

If you see them flying around your plants, one effective method for removing the flying ones is vacuum. Gnats suck at flying so they get easily sucked in if they fly anywhere near the vacuum.

The MOST effective thing for me has been to let the soil of the affected plants dry. So try to identify the most infested plants and reduce the frequency of watering for these (or all plants, ideally) - either wait until the top couple inches of soil are dry or until your plants starts complaining. When the soil dries up, the larvae can't survive & you can break the gnats' life cycle (if you also eliminate the adults with traps, vacuum, etc. before they make more larvae).

If none of this helps, you can always try replacing the soil of your most infested plants or go into chemical warfare. There is no shortage of insecticides that work on gnats, but those might also harm your plants and other living things.

I have had GREAT success using mosquito dunks. I get them at Agway or Blueseal, but they probably have them any home improvement or livestock supply place. They look like little donuts of gray grit. I break up a donut, stick a piece in my watering can, let it sit overnight to dissolve a little, then water as usual. And after a couple of weeks, the gnats are completely gone. The piece stays in the watering can and I just forget about it. Can't tell you how many times I've saved a hibiscus with this. It's what people use in horse watering troughs, bird baths and fish ponds to kill off mosquitos without harming the animals.

Of course, since joining this forum, I've learned the problem is poor soil and overwatering, but in the meanwhile, there's the dunks to help out. lol

From wikipedia on Mosquito dunks:

"Bacillus thuringiensis serovar israelensis (Bti) is a group of bacteria used as biological control agents for larvae stages of certain Dipterans. Bti produces toxins which are effective in killing various species of mosquitoes, fungus gnats, and blackflies, while having almost no effect on other organisms. Indeed this is one of the major advantages of B. thuringiensis products in general is that they are thought to affect few non-target species."

A slightly more detailed explanation of Bt's effect on affected insects and their larvae:

(excerpt from the Colorado State University Extension Office)

"Unlike typical nerve-poison insecticides, Bt acts by producing proteins (delta-endotoxin, the "toxic crystal") that reacts with the cells of the gut lining of susceptible insects. These Bt proteins paralyze the digestive system, and the infected insect stops feeding within hours. Bt-affected insects generally die from starvation, which can take several days. "

You should also purchase Stiky Sticks. Or yellow fly tape as these works wonders on catching they Adults. I find its best if you attack them from all angles by the Dunks killing the larvae and the Traps catching the adult flies!
Ive had fungus gnats for a while and have used the traps and have under watered a bit and theres bareley any anymore but hundreds on the traps.
I havnt been able to find Mosquito dunks though.... But when I do they all shall be gone!

I Know Nothing, I agree with Rhizo. Juice and sitting fruits attract fruit flies. I too wonder if you're seeing fruit flies or gnats.

I've heard people talk about fungus gnats flying around the house, and often wondered if these flying pests are truly gnats.
My plants are potted in soil, yet over the years I've never dwelt with flying fungus gnats.
During summer, when fruits are left out, 'we rarely run a/c,so house gets hot and humid,' fruit flies appear..but they don't bother plants.

I've seen gnats in green houses, especially after plants are watered..Their tiny, black/silvery hues are visible. They, however live in the soil.

The best way to rid or prevent fungus gnats is let soil dry between waterings, and run a ceiling fan. When it's warm out, open a window.

Yellow fly tape! On a side note - that stuff is strong. I made the mistake of hanging up some sticky fly rolls in the bathroom and kitchen years ago back before I knew about mosquito dunks. I could only hang them in those two rooms because those were places my parrot NEVER flew into. Of course two days of having the tape up, he just had to break his lifelong habits and it snagged him really well - stuck right to both wings and wouldn't let him go. It took forever to cut it all out of his caught feathers and a couple of months for him to look normal again. (At least now he is permanently terrified of the bathroom)

... I've never used anything sticky ever since.

Trillium...and they say cats are curious. lol

Your poor parrot. Getting stuck was one way for a wing clipping.
I've used yellow stick traps attached to plants, never in the air. My birds would have had yellow feathers.

Yellow traps work,,,and no chemicals. I've used them once, when an outdoor plant hosted whitefly. When I brought plants inside, they were loaded.
I placed sticky traps on various plants, within days white flies were history.

Mosquito Dunks work great for the larvae. You have to keep using it even when you finally get all the adults because some sneaky adult will lay eggs when you're not looking!

I'm gonna have to give this mosquito dunks thing a try too... btw MrBlubs, can get the stuff here: http://www.amazon.com/Summit-111-5-20-Pack-Mosquito-Dunk/dp/B0002568Y

this worked for me in a pinch when i had no other means of control (plants bought on a very long vacation):
put some dish soap in a sink of warm water: about 1tb per gallon. soak the pot submerged for 15 min. drain well.
take some shredded paper (or cut some tissue/newspaper with scissors, which is what i had to do) and put the shreds on top of soil, covering it. you will have to water around the shreds, they need to remain dry.
i did it once and had no more gnats.

Hi I know nothing (you will learn, lol)

I had a massive gnat problem for along time. I take it by now you have a large population? I had about 15 plants where the potting medium was alive! I tried traps, dips, larviecides..I tried and tried. If anything dunking caused alot of damage and I lost half my plants.

Easy cheap solution is to spinkle ant powder on top of your pottong medium, the gnats will pass the powder on to each other and the population will be exterminated very quickly, few hours.
I was worried the powder would get in to the root system but I was desperate and took the risk.
My plants are very healthy months on so the powder had no negitive effects.