Most reef tanks crash in the first six months. Here's why.

Six to eight weeks for a tank with no shortcuts. Add an ammonia source (pure ammonia or a raw shrimp), then test daily. The cycle is complete when ammonia and nitrite both read zero after you dose ammonia — not before. Bacteria seeding products can shorten the curve to three to four weeks in a best case, but you still need to verify with tests, not a calendar.

Alkalinity. It is consumed by coral calcification daily, fluctuates faster than calcium or magnesium, and wild swings cause bleaching and RTN faster than almost any other parameter error. Test alkalinity every one to two days when you have SPS coral, and dose to keep it within 0.5 dKH of your target.

Yes. Modern aquarium-specific LEDs — Radion, Hydra, Kessil — deliver the 420 nm and 450 nm spectra coral zooxanthellae use for photosynthesis. What matters is PAR (photosynthetically active radiation) at the coral's position in the tank, not the fixture brand. Target 50–150 PAR for soft coral and LPS, 150–350 PAR for SPS.

For most reef tanks, yes. A skimmer removes dissolved organic compounds before they break down into nitrate and phosphate. At low bioload and high water-change frequency you can run skimmerless, but most hobbyists find it harder to keep nutrients in range without one. Oversize the rated capacity by 30–50%.

Generally safe: clownfish, gobies, dartfish, basslets, cardinalfish, and most tangs. Risky: wrasses (some eat inverts), triggers (eat inverts and small fish), puffers (eat coral and inverts), lionfish (eat smaller fish). Individual variation exists — research the specific species, not just the family. Add fish after corals are established so territorial disputes favor the coral.