Keep your hands out of water for two hours after an manicure as water can cause polish to peel and avoid hot water to make the manicure last longer. Try soaking them in neat lemon juice for half an hour. If the yellowing is caused by nail varnish, don t remove it so often. Wear for a week and touch up as necessary. White marks on nails are caused by zinc deficiency.
Good sources are cheddar cheese and spinach.
Vertical ridges naturally occur on nails after the age of 40 or so. Massage your hands and nails daily to stimulate blood flow. Buffing nails also helps to reduce ridges. Alternatively you might like to use one of the ridge fillers currently on the market. A step by step guide to a perfect manicure.