Skimmer, RODI, lighting, flow, sump, test kit — what a reef really needs versus what it can skip.
6 questions, answered honestly and water-first.
On most reefs a skimmer earns its place by exporting waste before it breaks down, which helps keep nutrients in check. But it isn't strictly mandatory — lightly-stocked and nano tanks can run skimmerless on disciplined water changes. It's a very helpful tool, not a law.
Use RODI (reverse-osmosis / deionised) water. Tap water carries nitrate, phosphate, silicates and sometimes copper or metals that feed algae and harm inverts — exactly what you're trying to avoid. Mix your salt with RODI, or buy RODI saltwater ready-made.
It depends on the coral. Soft corals and most LPS are happy under modest reef light (~50–150 PAR); SPS need strong, high-quality light (~200–400 PAR). Match the fixture to what you plan to keep, and acclimate corals to new light slowly to avoid bleaching.
Enough to keep detritus from settling and to sway the corals, without blasting them. Soft corals and LPS want gentle-to-moderate flow; SPS want strong, turbulent, random flow. Aim powerheads to bounce off the glass rather than jetting one spot.
No, but it helps. A sump adds water volume (more stability), hides equipment, and gives you room for a skimmer and refugium. Plenty of successful reefs — especially nanos — run without one.
At minimum: salinity, and for a reef, alkalinity, calcium, magnesium, nitrate and phosphate; plus ammonia and nitrite while cycling. A good liquid test kit (and a refractometer for salinity) beats guessing from clear water — the numbers are the only honest read on your tank.
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Short answers from the Coralkin team — kind, general guidance, not a diagnosis. When something looks wrong, test your water first, and for a serious case ask an experienced reefer or an aquatic vet.
