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Fish and Aquarium・Invertebrates｜🔴 Supplementary Column A: Water Quality and Water Body Management
Water quality is not a subheading under husbandry but a medical subject in its own right — the chemical state of the whole water body acts on every individual in the tank at the same time. This chapter elevates the three stages of the nitrogen cycle into a full explanation, then threads each of six parameters — temperature, pH, ammonia with nitrite and nitrate, dissolved oxygen, salinity and hardness, chlorine and heavy metals — into a diagnostic chain of "what to measure, the direction of abnormality, what signs appear, and what the keeper should do". It establishes the order of investigation — test the water before you test the fish — and integrates the operating principles of the three pillars: water changes, filtration and the quarantine tank.
Fish and Aquarium・Invertebrates｜🔴 Supplementary Column A: Water Quality and Water Body Management
This content is compiled from the fish and aquarium / invertebrates chapter of the veterinary animal encyclopedia. The same sign calls for different handling in different species, and copying what is done for another species can be harmful — first confirm which animal you are dealing with.
Following the ruling in section four of `05-定序裁決與骨架修正-v2.md`, "group supplementary columns" are added beyond the 12 core columns, and those marked 🔴 are mandatory and cannot be omitted. This column applies to T3 ornamental fish and aquaria and to T9 ornamental invertebrates. Water quality is not a subheading under "husbandry"; it is a medical subject in its own right — section 4.3 of this text (husbandry environment) already covers the nitrogen cycle, water changes, the water parameter table, filtration, the quarantine tank and new tank syndrome, and what follows does not rewrite that material but elevates it out of the "environment" subsection and integrates it into a complete, self-contained diagnostic logic, filling in the parts that were not previously threaded together (the signs and actions matched one by one to the six parameters, and the principle of testing the water before the fish). The original text of sections 4.3 and 5.3.1 is retained unchanged, this column cross-references them, and no new figures are invented.
7.1 The nitrogen cycle and new tank syndrome (elevated from 4.3.1 and 4.3.7)
The greatest difference between a water quality problem and most other diseases: it is not a single pathogen invading a single individual but the chemical state of the whole water body acting on every individual in the tank at the same time — precisely why it must stand as its own column and why it is tightly linked with supplementary column B (flock-level, or in this case tank-level, handling).
| Stage | Substance produced | Toxicity to aquatic animals | Most dangerous moment |
|---|---|---|---|
| 1 | Ammonia (produced by the breakdown of waste and uneaten food) | Highly toxic | The earliest stage of a new tank, before the nitrifying bacterial population is established |
| 2 | Nitrite (formed as nitrifying bacteria oxidise ammonia) | Highly toxic | The "second wave" danger period, as ammonia begins to fall and nitrite rises in its place |
| 3 | Nitrate (formed by further oxidation of nitrite) | Less toxic, but still harmful when it accumulates over the long term | A long-term management issue once the tank is stable; the only effective way to remove it is a water change |
The essence of new tank syndrome is that the keeper puts too many fish or shrimp in during stages 1 and 2, before the bacterial population is fully established, leaving them soaking directly in ammonia and nitrite (see 4.3.1 and 4.3.7 for the mechanism, and item 1 of the disease table in 4.7).
7.2 The six parameters diagnosed one by one (what to measure／direction of abnormality／signs／what the keeper should do)
Specific value ranges are governed throughout by the table in 4.3.3 and its note that these are "ranges commonly recommended in the industry, not verified one by one"; this table does not repeat the figures and only fills in the diagnostic chain:
| Parameter | What to measure | Direction of abnormality | What signs appear in fish／invertebrates | What the keeper should do |
|---|---|---|---|---|
| Temperature | A water thermometer or the thermometer built into the heater | Too high, too low, or swinging sharply within a short time | Metabolic disturbance, stress, and reduced immunity triggering disease (white spot disease is strongly associated with sharp temperature swings, see item 2 of 4.7) | Use stable heating equipment and check regularly for failure (see "heater failure" in 4.10); avoid large temperature differences during water changes (see 4.3.2) |
| pH | A pH test kit or an electronic pen | Departure from the species' normal range, or sharp swings within a short time | Irritation of the mucous membranes and gills, stress, and in severe cases shock and death | Adjust slowly; abrupt changes are prohibited. If sharp swings are suspected, first test the pH of the water source itself |
| Ammonia／nitrite／nitrate | Test separately with the corresponding kits | Any detectable concentration of ammonia or nitrite is abnormal; persistently high nitrate must be dealt with by water changes | Rapid breathing, the group gasping at the surface, burn-like lesions of the gills, and large numbers dying simultaneously within a short time (new tank syndrome, see 7.1 and 4.3.7) | Immediately dilute with a water change and stop feeding; check whether the bacterial population in a new tank is not yet established; cycle the water first before stocking (fishless cycling) |
| Dissolved oxygen | A dissolved oxygen test kit or meter, or indirectly from the strength of aeration and flow | Too low | The group gathering at the air outlet and breathing hard; when signs affect the whole tank, suspect dissolved oxygen or ammonia／nitrite first rather than infectious disease (see the decision table in supplementary column B) | Increase aeration and flow; check whether overcrowding or an excessive water temperature is lowering the dissolved oxygen |
| Salinity, or hardness GH/KH | A hydrometer／refractometer (marine salinity); GH/KH test kits (freshwater hardness) | Sharp swings in salinity within a short time (marine); hardness too low or too high for the species' needs | Osmotic disturbance, stress, abnormal moulting (invertebrates, see item 1 of 5.7); when KH is too low, pH swings readily | Measure regularly with reliable instruments; when restoring salinity or hardness during a water change, do it slowly |
| Chlorine and heavy metals | A dechlorination test kit; heavy metals are not a routine test, but old pipework calls for heightened vigilance | Untreated chlorine／chloramine in tap water; elevated heavy metals such as copper ions | Burn-like gill damage; large numbers of invertebrates dying suddenly within a short time is the classic presentation of copper toxicity (see 4.10, 5.10 and item 2 of 5.7) | Treat with a dechlorinator before every water change without fail; never use copper-containing medication in a tank housing invertebrates (cross-reference section 8.4 of supplementary column B) |
7.3 Test the water before you test the fish
The first question most keepers ask when seeking help is "what disease does my fish have", but the correct first step is not to name the disease; it is to test the water:
- water quality abnormalities overlap heavily with several infectious diseases in their signs (gasping at the surface, rapid breathing, darkened colouration, refusal to feed, turning belly-up), and the signs alone cannot separate the two;
- a water quality problem can be fatal within hours to a day or two, and is usually more urgent than most infectious diseases;
- if you miss the water quality abnormality and treat a "disease" symptomatically, the medication itself is a second injury to an already stressed individual and does nothing about the true cause; and if invertebrates are housed in the tank, misusing copper-containing medication can wipe out every invertebrate in it (see 7.2 and 8.4).
Order of operations: first test ammonia／nitrite／nitrate／pH／dissolved oxygen／temperature (and salinity or hardness where needed) → only after confirming that water quality is normal do you move to the common disease table in the seventh column and work through the causes one by one. This order matters most of all when the whole tank is abnormal at once; see supplementary column B for detail.
7.4 Water changes, filtration and the quarantine tank — three operating pillars (integrated from 4.3.2, 4.3.4, 4.3.6 and 5.3.1; principles and direction only)
The figures below follow the original sections and are not reinvented:
- Water change: small and frequent beats one large change; the temperature difference between new water and tank water should be small; dechlorination is a mandatory step and cannot be skipped. Specific percentages and frequency: [Verification result: no fixed figure should be given for this item — it varies with the tank's bioload, and quoting a single figure as a general rule is not allowed] (see 4.3.2).
- Filtration: biological filtration carries the nitrifying bacterial population and is the physical substrate on which the nitrogen cycle runs; without it the cycle cannot be established. Mechanical filtration intercepts solid debris, and chemical filtration assists as required (see 4.3.4).
- Quarantine tank: any new individual should be observed in a separate system for a period before entering the main tank, the first line of defence against the double blow of "a new pathogen plus a new water quality shock" to the main tank. Specific day counts: [Verification result: no single authoritative figure — different teaching materials recommend different periods, and quoting a single day count as gospel is not allowed] (see 4.3.6).
Invertebrates (shrimp／snails／corals) have a lower margin for error than fish when it comes to water changes, filtration and water quality swings — a swing of the same magnitude that fish can ride out may be more than invertebrates can survive (see 5.3.1).
Limits of this content
This content comes from the fish and aquarium / invertebrates chapter of the veterinary encyclopedia (see the evidence chain for the original location and content hash). The sources at the end are the authoritative materials cited by that chapter; the correspondence is at chapter level, which does not mean every sentence is traced sentence by sentence back to a given source. This material is for education and cannot replace diagnosis and prescription by a practising veterinarian; in an emergency, seek veterinary care immediately. This text has not been clinically reviewed by a named veterinarian.
FAQ
- When a fish looks ill, what is the first thing to do?
- Test the water first, rather than looking for a disease name. Water quality abnormalities overlap heavily with several infectious diseases in their signs (gasping at the surface, rapid breathing, darkened colouration, refusal to feed, turning belly-up), the signs alone cannot separate them, and a water quality problem can be fatal within hours to a day or two. The order is ammonia, nitrite, nitrate, pH, dissolved oxygen and temperature; only after confirming that water quality is normal do you move to the common disease table and work through it.
- 魚が病気に見えるとき、最初に何をすべきですか。 — 病名を探すのではなく、まず水を測ってください。水質の異常と複数の感染症は症状が大きく重なり（水面での口ぱく、呼吸が速い、体色が暗くなる、餌を食べない、腹を上に向ける）、症状だけでは区別できません。しかも水質の問題は数時間から 1〜2 日で致命的になりえます。順序はアンモニア、亜硝酸塩、硝酸塩、pH、溶存酸素、温度で、水質が正常と確認できてはじめてよくある疾病表に進んで調べます。
- When a fish looks ill, what is the first thing to do? — Test the water first, rather than looking for a disease name. Water quality abnormalities overlap heavily with several infectious diseases in their signs (gasping at the surface, rapid breathing, darkened colouration, refusal to feed, turning belly-up), the signs alone cannot separate them, and a water quality problem can be fatal within hours to a day or two. The order is ammonia, nitrite, nitrate, pH, dissolved oxygen and temperature; only after confirming that water quality is normal do you move to the common disease table and work through it.
- When every fish in the tank goes wrong at once, what should be suspected first?
- Suspect a water body problem first — insufficient dissolved oxygen, or elevated ammonia and nitrite — rather than infectious disease. Immediately dilute with a water change and stop feeding, check whether the bacterial population in a new tank is not yet established, and check whether the heater or other equipment has failed.
- 水槽の魚が同時に不調になった場合、まず何を疑うべきですか。 — 感染症ではなく、溶存酸素の不足やアンモニア・亜硝酸塩の上昇といった水体の問題をまず疑ってください。このときはただちに換水して希釈し、給餌を止め、あわせて立ち上げ直後で菌群が未確立でないかを調べ、ヒーターなどの設備が故障していないかを確認します。
- When every fish in the tank goes wrong at once, what should be suspected first? — Suspect a water body problem first — insufficient dissolved oxygen, or elevated ammonia and nitrite — rather than infectious disease. Immediately dilute with a water change and stop feeding, check whether the bacterial population in a new tank is not yet established, and check whether the heater or other equipment has failed.
- Do invertebrates have the same margin for error as fish when water quality swings?
- No. Shrimp, snails and corals have a lower margin for error than fish when it comes to water changes, filtration and water quality swings; a swing of the same magnitude that fish can ride out may be more than invertebrates can survive. Sharp short-term swings in salinity or hardness also cause osmotic disturbance and abnormal moulting.
- 無脊椎動物の水質変動への許容度は魚と同じですか。 — 同じではありません。エビ、巻貝、サンゴは換水、ろ過、水質の変動に対する許容度が魚より低く、同じ幅の変動でも魚は乗り切れて無脊椎動物は乗り切れないことがあります。塩分濃度や硬度が短時間に激しく変動すると、浸透圧の失調や脱皮の異常も生じます。
- Do invertebrates have the same margin for error as fish when water quality swings? — No. Shrimp, snails and corals have a lower margin for error than fish when it comes to water changes, filtration and water quality swings; a swing of the same magnitude that fish can ride out may be more than invertebrates can survive. Sharp short-term swings in salinity or hardness also cause osmotic disturbance and abnormal moulting.
Source anchors
- openlibrary.org｜魚類與水族・無脊椎章引用 · https://openlibrary.org/works/OL19509478W · 在 IDAEO 的其他引用
- openlibrary.org｜魚類與水族・無脊椎章引用 · https://openlibrary.org/works/OL21421796W · 在 IDAEO 的其他引用
- www.wavma.org｜魚類與水族・無脊椎章引用 · https://www.wavma.org/ · 在 IDAEO 的其他引用
- 本文證據鏈：原始章節位置與內容雜湊 · https://km.idaeo.ai/reports/vet-water-quality-management-evidence · 在 IDAEO 的其他引用
Cite this article
獸醫百科編輯部・《Fish and Aquarium・Invertebrates｜🔴 Supplementary Column A: Water Quality and Water Body Management》・IDAEO 知識庫・2026-08-13・https://km.idaeo.ai/post/vet/water-quality-managementUpdated 2026-08-14