Fish lying on substrate has 2 categories: normal vs alarming. Normal substrate-resting: 1) Plecos + loaches + Otocinclus rest on substrate during day. 2) Bettas often rest on leaves or substrate at night. 3) Goldfish may rest at night. 4) Fancy goldfish (oranda, ranchu) sometimes rest from buoyancy issues. 5) Newly-acclimated fish may rest 1-2 days while adjusting. Alarming if NEW behavior: 1) Fast breathing + bottom-resting = water-quality issue. Test ammonia (target 0), nitrite (target 0), nitrate (target <30 FW, <10 reef). 2) Color fade + lethargy + bottom-rest = stress, disease, or end-stage condition. 3) Visible parasites (white spots, gold dust) + bottom-rest = ich/velvet. 4) Pinecone scales + bottom-rest = dropsy (often fatal). 5) Belly swollen + bottom-rest = constipation or internal infection. Diagnostic protocol: 1) Test water immediately. 2) Inspect for visible parasites or wounds. 3) Note rapid breathing rate (count gill movements per 10 sec - >40 is rapid). 4) Check for missing tankmates that may have died. 5) Use our symptom matcher to rank causes. 6) Quarantine + treat based on findings.
The full Q&A library, calculators, diseases, glossary, and interactive tools answer the most-searched aquarium questions.
Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.
How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.
What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.
How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.
Saltwater livestock · Freshwater livestock · Coral catalog · Care library · Q&A library (222) · Glossary (127) · Disease database (50) · Calculators (29) · Interactive tools (7) · Husbandry deep-dives · DIY projects · State legality directory