Troubleshooter

Why is my fish eating the substrate?

Quick answerBottom-dwelling fish (corydoras, plecos, loaches) sift substrate looking for food. Some fish (cichlids) move substrate as territorial behavior. Most cases are normal; concern only if fish actually ingests gravel.

Possible causes (4)

1. Normal sifting behavior

Corydoras + plecos sift substrate searching for food particles. Spit out gravel + ingest food. Completely normal.

2. Territorial cichlid behavior

Cichlids redecorate by moving substrate. Normal pre-spawning + territory marking.

3. Hunger

Underfed fish search the substrate harder. Increase feeding if behavior is excessive.

4. Geophagy (gravel ingestion)

Some fish actually eat gravel intentionally. Sand is safer than gravel - switch substrate if ingestion is observed.

What to do next

Test water first - many "behavior" issues are actually water-quality problems. Use the water parameter checker to score your test results, the disease symptom matcher if you observe physical signs, or the general diagnoser to narrow further. Browse the disease database if illness is suspected.

More troubleshooting

Browse all behavior troubleshooting articles.

Aquarium-keeping fundamentals

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.

Frequently asked questions

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.