In some parts of the world, local effects can mean only one tide a day, or even none. Between the two bulges are two troughs of low water, producing two low tides a day. Springs and neaps Tides change in height - low water level and high water level vary throughout the month. The tides build up to a maximum and fall to a minimum twice a month. The tides with the biggest difference between high and low water are called springs and those with the smallest are called neaps.
Spring tides happen just after every full and new moon, when the sun, moon and earth are in line.
That's when lunar and solar tides line up and reinforce each other, making a bigger total tide. Neap tides occur when the moon is in the first or third quarter - when the sun, earth and moon form a right angle. The lunar high tide coincides with the solar low tide and they partly cancel out, giving a small total tide. The regular motion of the sun, moon and earth cause spring tides to occur roughly 36 to 48 hours after the full or new moon, and for any given location, always at roughly the same time of day. For example at Liverpool, the spring tides are generally around midnight and midday.