Potassium permanganate is the remedy used on this for decades. This is poison, yet used externally, it seems to be one of the best solutions to the problem. Permanganate is a powerful fungus killer! And fungus under the nails demands something very special. The permanganate also stains the skin dark brown, so after soaking your toes or feet in the solution, they will not look very pretty. Formula: Soak the feet for half an hour in a warm 1:5,000 solution of potassium permanganate. Dry the feet thoroughly after use. This is the same formula for athlete's foot, which is a similar fungal foot disease.
If you need to prepare this solution at home, you dissolve a slightly rounded teaspoon of the crystals in 8 ounces of water. Keep it in a dark-colored glass bottle. A teaspoon of this saturated solution in a pint of water makes a solution of about 1:1,500 strength; a teaspoon in a quart of water makes one of about 1:3,000 strength. With this information, you will be able to prepare about any strength you might need.