Guides
Aquarium guides
What you need to know to keep a tank, one thing at a time. The reference values are the same ones the app uses to tell you whether a parameter is in range: the site and the app never give you two different answers.
One note before you act on any of this. Every tank is its own case: the values on these pages are reference ranges, not prescriptions. If your animals are suffering, move in small steps and measure before correcting — a fast correction almost always does more damage than the wrong value did.
Starting up and the nitrogen cycle
The first weeks of a new tank: what happens in the water, what to measure and when the first fish can go in.
Fishless cycling: how much ammonia to dose
Cycling an aquarium without fish: which ammonia to use, how much to dose, how to keep it topped up and how to know the cycle is finished. With the dose calculation.
New tank syndrome: symptoms and what to do
Fish in a new tank are sick or dying: how to recognise new tank syndrome, what to test straight away and how to limit the damage.
Starting a freshwater aquarium: the first six weeks
What to do week by week in a new freshwater tank: setup, growing the bacteria, the first test readings and when the first fish can go in.
Starting a saltwater aquarium: live rock, dry rock or a deep sand bed
How a marine tank is started: live rock versus dry rock, the salinity to hold, how long maturation takes and the order in which fish and corals go in.
The aquarium nitrogen cycle: what it is and how long it takes
What the nitrogen cycle is, how long it really takes and how to tell when a tank is ready for fish. With the values to check week by week.
Water parameters
One parameter at a time: what it measures, which values to hold and what to do when they drift.
Ammonia in an aquarium: why it is the most dangerous
What ammonia is in an aquarium, why it kills, where it comes from and what to do when the test detects it. With the role of pH and temperature in its toxicity.
Aquarium pH: ideal values and how to correct it
Which pH to hold for each type of tank, why it swings over the day, and why correcting it directly is almost always a mistake. What to do instead.
Aquarium temperature: which one for which fish
What temperature to hold for each type of tank and fish, why swings matter more than the value, and what to do when the water gets too warm in summer.
Aquarium water change: how much, how often, how
How much water to change and how often, how to prepare the new water and the steps to do it without stressing the fish. With the arithmetic of the effect on nitrate.
Calcium, KH and magnesium in a reef: the triangle
Why calcium, alkalinity and magnesium move together in a reef, which values to hold, and why when calcium or KH will not come up the culprit is nearly always magnesium.
High nitrate: how to lower it for real
Why nitrate climbs in an aquarium, which values to hold in freshwater and in a reef, and the methods that actually lower it — from water changes to plants.
High nitrite in an aquarium: what to do right now
Nitrite above zero: why it is an emergency, what to do in the next few hours and the next few days, and how long it takes to fall back to zero on its own.
How to read a liquid test kit without getting it wrong
Liquid test kits go wrong less often than the people reading them: light, background, angle, waiting times, expired reagents and the traps of each individual kit.
Phosphate and algae: the link nobody explains
Why high phosphate feeds algae, where it comes from, which values to hold in freshwater and in a reef, and why driving it to zero does not solve the problem.
Salinity: ppt, specific gravity and mS/cm compared
The three units of salinity and how they convert: ppt, specific gravity and conductivity. Which value to hold in a reef, how to measure it and calibration errors.
Water hardness: GH and KH explained simply
GH and KH are not the same thing: what they measure, which values fish and shrimp need, and how to raise or lower them without doing damage.
Problems and diagnosis
Something is wrong right now: how to read the symptoms and where to start.
Aquarium algae: identify them by colour and get rid of them
How to recognise aquarium algae by colour and texture — brown, green, hair, black brush, cyanobacteria — and what to do about each of them.
Cloudy or milky aquarium water: the 5 causes
Aquarium water gone cloudy, milky, green or yellow: how to tell a bacterial bloom from suspended substrate, and what to do in each case.
Fish gasping at the surface: what to check
A fish sitting at the surface with its mouth open has an oxygen or a gill problem: the seven causes in order of likelihood and what to do in the first few minutes.
Why new fish die soon after you buy them
New fish die in the first days: the real causes in order of frequency, how to acclimatise a fish properly and what to do before buying any more.
Charts and tools
Pages you come back to: reference values, how many fish fit, who lives with whom.
Freshwater fish compatibility
How to decide whether two freshwater fish can live together: water, volume, temperament and size, with the four checks to run before buying.
How many fish in a 60, 100 or 200 litre tank (16, 26, 53 gal)
How many fish actually fit, with the calculation model explained and its assumptions: capacity in centimetres of fish per litre, by type of tank.
Ideal water parameters chart by type of tank
The reference values of every water parameter, for freshwater, planted, brackish, marine and reef tanks, in one chart you can come back to.