Start with what you can see
Six symptoms account for most of what brings people here. None of the pages behind them is written yet, so they are listed rather than linked, and the answer we can give today sits underneath each one.
The order we check things in
This is the method every guide in this topic will follow, and publishing it before the guides exist is the point: if a page here ever skips a step to reach a product, you can hold it against this list.
Temperature, before anything
It is the cheapest thing to check and the most common cause. Every species record on this site states a range, and a fish below its range slows down, eats less and gets sick more easily. A thermometer answers more questions than a test kit.
The tank, not the fish
Volume, stocking and how long ago the water was changed. A five gallon has no dilution to hide behind, which is why the same mistake reads as a crisis there and as a Tuesday in twenty gallons.
Physical causes, before chemical ones
Sharp decor, strong surface flow, gravel under a fish that feeds with barbels, a lid that lets the air above the water go cold. Most torn fins and most hiding are furniture problems.
Then, and only then, water chemistry
pH and hardness are the fields keepers reach for first and the ones that are least often the cause. Our records give wide tolerances for both, which is precisely why chasing a decimal is rarely the fix.
Medication last, and not from us
We will publish what our sources state about husbandry. We will not print dosages, treatment schedules or disease diagnoses, because no source we compile from states them in a form we could stand behind, and a wrong number here costs an animal.
What this topic will and will not carry
Will carry
- Husbandry causes and fixes that a named source states: temperature, volume, substrate, flow, feeding, cover.
- The order to check them in, so a symptom page reads as a diagnosis rather than a list.
- Cross links to the records, because the range a species actually wants is the reference point.
- The blanks, in the same way the records carry them.
Will not carry
- Medication dosages or treatment schedules. Not now, not later.
- Disease diagnosis from a photograph, which is the most requested and least defensible thing in this topic.
- Product affiliate links inside a symptom page, where a worried keeper will click anything.
- Numbers from forums, which is where most of the figures in this topic circulate.
Every record, on the three water parameters we hold
This topic is about numbers, so here are all of them. Every care record on the site, against temperature, pH and hardness, with the blanks printed as blanks.
| Field | African dwarf frog | Amano shrimp | Angelfish | Assassin snail | Axolotl | Betta | Black molly | Bristlenose pleco | Celestial pearl danio | Cherry shrimp | Chili rasbora | Chinese algae eater | Clown killifish | Clown loach | Common pleco | Corydoras | Damselfish | Discus | Dojo loach | Ember tetra | Flowerhorn | German blue ram | Ghost shrimp | Goldfish | Guppy | Honey gourami | Kuhli loach | Least killifish | Mandarin goby | Nerite snail | Oscar fish | Otocinclus | Pea puffer | Platy | Rabbit snail | Ramshorn snail | Redtail catfish | Siamese algae eater | Sparkling gourami | Vampire shrimp |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temperature | 73 to 79 °F | 72 to 78 °F | 78 to 84 °F | 75 to 80 °F | 61 to 64 °F | Around 80 °F | 72 to 78 °F | 74 to 79 °F | 73 to 76 °F | 59 to 86 °F | 72 to 82 °F | 77 to 79 °F | 68 to 79 °F | 82 °F | 72 to 86 °F | 72 to 82 °F | 73 to 81 °F | 85 to 86 °F | 68 to 72 °F | 72 to 82 °F | 80 to 86 °F | 84 to 85 °F | 72 to 80 °F | 68 to 74 °F | 63 to 82 °F | 74 to 81 °F | 74 to 79 °F | 75 to 78 °F | 76 to 82 °F | 72 to 79 °F | 75 to 80 °F | 70 to 79 °F | 74 to 82 °F | 70 to 77 °F | 78 to 84 °F | 70 to 78 °F | 72 to 76 °F | 75 to 79 °F | 77 to 80 °F | 74 to 84 °F |
| pH | 6.5 to 7.5 | 7.2 to 7.5 | 6.5 to 7.5 | 7.0 to 7.5 | 7.4 to 7.6 | 6.0 to 8.0 | 7.5 to 8.5 | 6.5 to 7.5 | 6.6 to 7.5 | 6.5 to 8.0 | 6.0 to 7.0 | 6.0 to 8.0 | 4.0 to 7.0 | 6.0 to 7.0 | 6.5 to 7.5 | 6.5 to 7.8 | 8.1 to 8.4 | 6.8 | 6.5 to 8.0 | 5.5 to 7.0 | 7.0 to 7.5 | 6.0 to 7.0 | 7.0 to 8.0 | 7.0 to 8.4 | 7.0 to 8.5 | 6.0 to 7.5 | 3.5 to 7.0 | 7.0 to 8.0 | 8.1 to 8.4 | 7.5 to 8.5 | 6.0 to 8.0 | 6.0 to 7.5 | 6.8 to 8.0 | 7.0 to 8.0 | 7.5 | 7.0 to 7.5 | 6.0 to 6.8 | 6.5 to 7.5 | 6.0 to 7.0 | 7.0 to 7.2 |
| Hardness | 89 to 358 ppm | 72 to 251 ppm | 89 to 215 ppm | 107 to 268 ppm | 125 to 250 ppm | 18 to 268 ppm | 268 to 536 ppm (15 to 30 dGH) | 71 to 200 ppm | 89 to 179 ppm (5 to 10 dGH) | 71 to 179 ppm | 54 to 179 ppm | 89 to 321 ppm | 18 to 143 ppm | 71 to 214 ppm | Up to 446 ppm (25 dGH) | 18 to 268 ppm | Specific gravity 1.020 to 1.025 | 18 to 70 ppm | 89 to 214 ppm | 18 to 179 ppm | 161 to 358 ppm | 18 to 179 ppm | not recorded | not recorded | 143 to 536 ppm | 71 to 214 ppm | 0 to 143 ppm | 89 to 357 ppm (5 to 20 dGH) | Specific gravity 1.025 | 215 to 322 ppm | 215 to 268 ppm | 36 to 179 ppm | 90 to 448 ppm | 214 to 321 ppm | 107 to 143 ppm | 143 to 322 ppm | 54 to 214 ppm | 71 to 268 ppm | 89 to 214 ppm (5 to 12 dGH) | 107 to 357 ppm (6 to 20 dGH) |
What the table says about hardness
Hardness is the row keepers skip and the row with the widest spread on it. The fish records tolerate almost anything: the betta is recorded from 18 to 268 ppm, the ember tetra 18 to 179, the kuhli loach 0 to 143. None of those pages attaches a consequence to the number.
One record does. The cherry shrimp grows by molting, which means it builds a shell out of minerals taken from the water, and its source publishes GH 4 to 10 for that reason. It is the only animal on this site where hardness is a requirement rather than a tolerance, and it is the reason a GH test is worth owning even in a fish only tank: you cannot know which of those two situations you are in without one.
What the table says about pH
Read the pH column and the spread is enormous, from 3.5 on the kuhli loach page to 8.5 on the guppy. That is not an invitation to chase a decimal. It is evidence that pH is the parameter most often blamed and least often the problem.
The kuhli loach floor of 3.5 is the clearest case. It is a blackwater tolerance recorded from a habitat of forest streams over decaying leaves, not a target for a tank, and reading it as a target is how people end up dosing acid into stable water.
One aquarium, one temperature
Stack every recorded range and the overlap is the setting a mixed tank can actually run at. This is the same chart the fish silo carries, drawn across every record on the site rather than one silo.
Stacked across every record on this site there is no band left at all, and ten records are why. The axolotl ceiling is 64 °F, the dojo loach ceiling is 72, the goldfish ceiling is 74, the angelfish floor is 78 and the rabbit snail floor is 78 as well, the flowerhorn floor is 80, the german blue ram floor is 84, the discus floor is 85, and our chinese algae eater record misses by a single degree with a floor of 77, and the clown loach record prints one figure, 82, with nothing either side of it.
Take those ten out and the remaining twenty seven overlap from 75 to 76 °F, set at the bottom by three records together, the oscar, the assassin snail and the siamese algae eater, and at the top by one, our redtail catfish record, which stops at 76. That ceiling has moved twice, and each time one record took a degree off the whole site: it was 78 and the amano shrimp until the platy record was written, then 77 and the platy and water sprite records together, and now 76, because the five sources on the largest fish here meet at 72 to 76.
The site now spans 61 to 86 °F end to end, and the tightest band on it is the discus at a single degree, 85 to 86, with the clown loach tighter still at a single figure: 82 °F, because that is the only temperature its five sources all allow. At the other end three records tolerate 59 to 86: the cherry shrimp, the hornwort and the java moss.
Two things follow. A heater is not a question of whether the species needs warmth, it is a question of whether your room holds a number inside the band without help. And the case for one species per layer is partly thermal: the more records you stack, the narrower the shared band gets, and it can close entirely.
Questions about aquarium water parameters
What temperature suits every species on this site?
None, and that is the answer rather than a gap. The axolotl stops at 64 °F, the dojo loach at 72, the goldfish at 74, the angelfish and the rabbit snail do not start until 78, the german blue ram not until 84 and the discus not until 85, so no single setting suits every record on this site. Without those ten the remaining twenty seven share 75 to 76 °F, capped by the platy, with the amano shrimp one degree behind it at 78. Smaller combinations have more room: betta, ember tetra and corydoras overlap from 72 to 82.
Does water hardness matter, or is it just pH?
It matters for two animals on this site and is a tolerance for the rest. The cherry shrimp molts continuously and its source publishes GH 4 to 10 as the requirement behind that. The nerite snail builds a shell out of the same minerals and no source we name publishes a figure for it at all, which is why that cell is blank. The fish records give hardness as a range they tolerate, up to 448 ppm on the pea puffer record, with no consequence attached to where in the range you sit.
What pH should I aim for?
A number inside the range on your species record, held steady. Our records span 3.5 to 8.5 across forty eight animals, which tells you the useful thing: the spread is wide, so stability is worth more than a target. Nothing on this site asks you to move a stable pH.
Why does this site not publish medication advice?
Because no source we compile from states dosages or treatment schedules in a form we could stand behind, and a wrong number in this particular subject costs an animal. We publish what our sources state about husbandry, which is the part that prevents most of what medication is bought for.
A fish is sitting on the bottom. What do I check first?
Temperature, before anything else. It is the first item in the order above, and it is the cheapest to check and the most common answer. The betta record puts it plainly: the bottom of that species' range is where the sitting on the bottom stories come from.
How do I know whether my water is too soft?
A GH test, which is a different test from pH and usually sold separately. Reverse osmosis water and naturally very soft tap water sit under the GH 4 to 10 the cherry shrimp record asks for, and crushed coral in the filter or the substrate is the stated way to raise it. For the nerite snail the sign comes before the test: its source attributes cracked or eroded shells to soft tap water.
Do I need a heater?
It depends on the room rather than on the fish. If your room sits inside the range on the record without help, no; if it swings through it, yes, because holding one number is easier than hitting one. Three records tolerate 59 to 86 °F, the widest we hold: the cherry shrimp, the hornwort and the java moss. The narrowest by a distance is the discus at 85 to 86, a single degree, which is what the overlap of four published bands came to.
What is TDS and do I need to measure it?
Total dissolved solids, and only one of our sources publishes a figure for it: Shrimp Science gives 100 to 250 for the cherry shrimp. No fish record we hold states a TDS range, so this site does not ask you to measure something it cannot give you a target for.
My water went cloudy. What does this site say?
Nothing yet, and that is the honest answer: the guide is in the queue below rather than written. White haze, a green tint and a sudden bloom have different causes and telling them apart is the whole of the first step, so a page that treated them as one problem would be worse than no page.
Do I have to test everything?
Test what your records turn on. For the fish on this site that is temperature, and pH only far enough to know it is stable. For the cherry shrimp it is GH, which is the field its shell is made of. Nothing on this site asks for a test whose result it cannot tell you what to do with.
What is not here yet
Nine guides in the queue
Ordered by how often they are searched. Each one waits on a source that states husbandry causes rather than a product, which is why this topic moves slower than the species records.
Ammonia, nitrite and nitrate, and a source that disagrees about all three
This topic carries the three water fields every record on this site holds: temperature, pH and hardness. It does not carry the nitrogen cycle, because no species care source we compile from states an ammonia figure for a species. They state what the animal wants; nobody publishes a per species toxicity threshold.
That is a real gap and this page is not going to leave it as a silence, because two sources in the same reading disagree about the numbers in a way a keeper needs to see.
The consensus figure, and the one that argues with it
LiveAquaria gives the answer every chart in every aquarium shop gives: ammonia 0.0 ppm, nitrite 0.0 ppm, nitrate under 50 ppm, in a freshwater community tank held at 72 to 82 °F and pH 6.5 to 7.5, with 4 to 8 KH and 4 to 12 GH.
Aquarium Science, which this site already cites on the nerite record for general hardness, gives different numbers and a different reason for them. Ammonia and nitrite should always be 0.25 or lower on an API test rather than zero. Nitrate it calls relatively non toxic, and states that 880 ppm is survivable for most fish.
Why the reason matters more than the number
Aquarium Science does not treat these readings primarily as poisons. Its sentence is that a reading of ammonia or nitrite indicates poor biofiltration which will kill fish from excess bacteria in the water. On that reading the number is a symptom of a filter that is not working rather than the thing doing the damage, which changes what you do about it.
It does also give the acute figures, at pH 7.0: ammonia at 5 ppm causes death in hours or days, and nitrite is acutely toxic at 2 ppm. Chlorine it puts far lower, toxic in the order of 0.05 ppm, which is the argument for treating tap water rather than testing it.
The figure that contradicts the whole hobby
Aquarium Science states that an aquarium needs to be established for three or four months before zero ammonia and zero nitrite can be achieved. Most cycling advice is measured in weeks. We are not going to adjudicate that, and it is the single most consequential disagreement on this page: it is the difference between adding fish next month and adding them next season.
What every record here already says points the same way. The cherry shrimp record names a brand new tank as its second most common failure, and the otocinclus record puts a tank with nothing growing in it first. Neither of those is a chemistry argument, and both are describing a tank that has not been established long enough.
| Reading | LiveAquaria | Aquarium Science |
|---|---|---|
| Ammonia | 0.0 ppm | 0.25 or lower |
| Nitrite | 0.0 ppm | 0.25 or lower |
| Nitrate | under 50 ppm | relatively non toxic, 880 ppm survivable |
| Ammonia, acutely toxic at | not stated | 5 ppm at pH 7.0, death in hours or days |
| Nitrite, acutely toxic at | not stated | 2 ppm |
| Chlorine, toxic at | not stated | about 0.05 ppm |
| Time to reach zero | not stated | three to four months established |
Read that table and the honest summary is that the nitrogen cycle is the least settled thing on this site, and it is the one most often presented as settled everywhere else. Neither figure goes into a record field, because a field on this site belongs to a species and neither source is talking about a species. What goes in the fields is temperature, pH and hardness, and those are in the grid above with a source on every one.
Guides on this topic
This topic carries the three water fields every record holds. A guide is where a question that is not a figure gets answered. Two of the three here are about food, what to feed a snail and what shrimp eat when nobody feeds them, and both ran into the same wall: no source we compile from will publish a feeding schedule for a scavenger. The third is about water, and it is here because a genus figure and a species figure contradict each other: our apistogramma guide carries a recommended 80 to 82 °F for the genus against 68 to 79 °F published for one of the two species people buy most.