Saxby's principle — water comes first
“In a reef aquarium, you do not keep animals — you keep water. If the water is right, everything else follows.” — David Saxby
David Saxby is one of the most respected figures in Western reefkeeping. His most famous reef ran for over twenty years without dramatic crashes or repeated resets. His lesson is simple but hard to internalize: a hobbyist who focuses on animals before water ends up chasing symptoms rather than fixing causes.
What the principle means in practice
The animals in a reef aquarium — corals and fish — have evolved to live in seawater of remarkably constant composition. On the open reef, alkalinity, calcium, magnesium, salinity and temperature vary only marginally over months and years. So the animals are not adapted to “good water” — they are adapted to stable water.
In an aquarium this translates into something concrete: if the water is chemically, physically and biologically balanced and stays that way, the animals largely take care of themselves. If the water swings, no single additive, medication or device will permanently fix the situation.
Why this is hard to accept
Reefkeeping is marketed around the animals: glossy photos of colourful Acropora, expensive fish, elaborate aquascapes. Water is invisible and undramatic. A hobbyist who has spent thousands on animals naturally wants to focus on them.
But water is the precondition for everything else. The best lighting will not save a coral if alkalinity drifts 1.5 dKH within a day. The most skilled fish keeper cannot keep an Anthias shoal healthy in a tank where oxygen drops below 6 mg/l at night.
Practical consequences for a beginner
This principle drives concrete decisions before the first coral is even purchased:
- RO/DI before lighting. Water is the first investment, not the last. Finnish tap water contains chlorine, fluoride, heavy metals and variable nutrients — you cannot build a stable reference on top of it.
- Measure before adding. A monthly ICP test tells you which direction the water is moving. Without data, dosing is guesswork.
- One variable at a time. If you change three things at once and the tank improves or declines, you do not know which change did it.
- Stability beats “ideal value”. Alkalinity at 7.5 dKH every day is better than 8.5 one day and 7.0 the next.
What you gain
Once the water is under control, the hobbyist is freed. Time stops being consumed by constant crisis management — dipping sick corals, fighting algae outbreaks, medicating fish. The job becomes keeping the water good, and the rest mostly takes care of itself.
That is Saxby’s promise, and the reason this site is built around water chemistry. Start with what surrounds the animal, and the choice of animals becomes almost a matter of taste.