When the lowest tides happen and why
Tide pools are only tide pools when the tide is out. The rest of the time they're submerged shelves, indistinguishable from the ocean above them. So the question for anyone who wants to look at sea anemones, hermit crabs, sculpins, or the dozens of other species that live in the intertidal zone is simple: when does the water leave, how far down does it go, and how long do I have to walk around before it comes back. The answer depends on the moon, the geometry of your coastline, and a forecasting method called harmonic prediction that has been refined over a century and works very well.
Spring tides are when the bottom drops out
Around new and full moons, the gravitational pull of the sun and the moon line up. Highs go higher, lows go lower. These are spring tides. The lowest lows of any month happen during the spring-tide window, usually within a day or two of the exact phase. For tide pooling, this is the only window worth your trouble: a typical day's low tide might leave a thin strip of seaweed-covered rock visible at the foot of a cliff, while a spring low pulls the water back fifteen or twenty metres further, exposing whole platforms of pools that haven't seen air in two weeks.
Neap tides are the off-weeks
The opposite of a spring is a neap. Around the first and third quarter of the moon, the sun and moon are pulling at right angles to each other — one going up while the other goes down. The tides cancel partially. Highs are lower, lows are higher, the swing is at its smallest. During a neap-tide week, even the lowest predicted low won't expose much that wasn't already exposed at average tides. If the only days you can make it to the coast fall during a neap week, do something else. The pools won't show.
How predictions actually work
The numbers on this site come from harmonic prediction — a mathematical method that models the tide at a specific gauge as the sum of dozens of pure sine waves, each with a known astronomical period. The biggest wave is the principal lunar semidiurnal, M2, with a period of about twelve hours and twenty-five minutes. Each gauge has its own set of harmonic constants, fitted from years of measured water-level data. Once you have the constants, you can predict the tide at that gauge for any date forward or backward, accurate to a few centimetres and a few minutes under normal weather. Storms add surge that the math doesn't see, but the astronomical signal is as predictable as the moon phase itself.
Reading the seven-day table
On every place page on this site, there's a seven-day high-and-low table. For tide pooling, ignore the highs and look at the lows. Pick the lowest one of the week. Compare its time to the sunrise and sunset on the sun-and-moon block: a low at 04:30 in winter is dark, useless. A low at 09:00 in summer is perfect. The window is roughly an hour either side of the printed time — that's how long you have to walk out, look around, take photos, and walk back before water starts covering things again. Don't push it, the flood comes faster than the ebb.
Where the species are
The intertidal zone is split into bands. The high-tide band — barnacles, periwinkles, dry rock for hours each day — is exposed even on average tides. The mid band — mussels, limpets, some anemones — shows on most low tides. The low band — the interesting stuff, the bigger anemones, sea stars, hermit crabs, occasional small fish trapped in pools — is exposed only on spring lows, and only briefly. That's the band you've come for. Step carefully, don't pry anything off the rock, and put rocks back the way you found them. The species there are tougher than they look but slow to recover from being mishandled.