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If you keep stony corals, three numbers matter more than almost anything else in your tank: calcium, alkalinity, and magnesium. Reef keepers often call them “the Big 3” because every SPS and LPS coral, every bit of coralline algae, and most of your invertebrates depend on a steady supply of these three elements to build their skeletons. Get them right and your reef grows, colors up, and stays stable for years. Get them wrong — even slightly — and you’ll spend your hobby chasing stalled growth, bleached tips, and mysterious coral deaths that always seem to trace back to water chemistry.

Designing an aquarium is as rewarding as it is challenging, blending creativity with precise care. Selecting the ideal components and digital tools in advance can spare frustration later and set the stage for a thriving aquatic ecosystem. This guide walks through key steps—from choosing tank size to selecting fish—equipping hobbyists with the insights needed to confidently craft their own underwater world.