Aquarium Water Chemistry and Setup Guides

What water parameters does every aquarium keeper need to understand?

Every aquarium keeper needs to understand five things about tank water: temperature, pH, hardness, the nitrogen compounds (ammonia, nitrite and nitrate) and, for shrimp and planted tanks, dissolved solids and carbon dioxide. A water parameter is any measurable property of the water that affects whether a species can live in it. The table gives one published reference value for each and the guide that explains it.

In what order should a beginner read the guides?

A beginner should read the guides in the order a tank is built: cycle first, then water, then fish, then routine care. Each step depends on the one before it, so reading out of order tends to produce the classic mistake of buying fish for an uncycled tank. The recommended reading order is set out below.

1. The aquarium nitrogen cycle. How bacteria turn ammonia into nitrite and nitrate, and why a new tank is unsafe until they do.
2. The fishless cycling method. How to grow those bacteria with dosed ammonia before any fish arrive, and how to tell when the cycle is complete.
3. How to prepare tap water for aquariums. Chlorine, chloramine and what a conditioner must remove from every refill.
4. The aquarium temperature chart. Tropical versus coldwater fish, and how to set a heater for a mixed tank.
5. The aquarium pH guide. What pH measures, the ranges species need and why stability matters more than a target number.
6. The general and carbonate hardness explainer. Soft versus hard water and how KH holds pH steady.
7. The guide to acclimating new fish. Float and drip methods for moving fish from the bag into the tank.
8. The weekly aquarium maintenance schedule. Water changes, testing and filter care once the tank is stocked.

After these eight, a keeper who wants live plants moves on to the planted-tank guides, and a keeper who wants shrimp reads the TDS and RO guides. Both groups are covered further down.

How do water parameters decide which fish can share a tank?

Water parameters decide which fish can share a tank because two species can only live together inside the range both tolerate. Temperature, pH and hardness are three of the six factors in every AquaCompat pair score, and the shared band of two ranges is the figure that matters, not either range alone.

The soft-versus-hard split shows how large the differences are. The Neon Tetra is listed at pH 5.0–7.5 and 1–12 dGH, while the Molly needs pH 7.5–8.5 and 15–25 dGH. The two share almost no water, however peaceful both are. A Corydoras at pH 6.5–7.5 sits between them and overlaps both.

Temperature splits species in the same way. The goldfish at 59–70 °F (15–21 °C) and the discus at 79–86 °F (26–30 °C) have no temperature in common at all. The two-species compatibility checker prints the shared range for any pair, and the fish compatibility guides explain each pairing in full. The scoring rules themselves sit on the methodology page.

How long does it take to set up a new aquarium?

Setting up a new aquarium takes several weeks before the first fish, because published sources give between 4–6 weeks and 6–8 weeks for the nitrifying bacteria to establish. The sources disagree on the exact figure, and the spread is worth knowing.

• UF/IFAS Extension gives 6–8 weeks for a new biofilter, and the Merck Veterinary Manual gives 6–8 weeks.
• Practical Fishkeeping says most tanks take 4–6 weeks.
• Dr Tim's Aquatics, which sells a bacteria starter, gives 30–45 days for a fishless cycle without its product.

Rather than counting days, the cycle is complete when a dose of ammonia clears to zero ammonia and nitrite within 24 hours, the test both Dr Tim's and Practical Fishkeeping use. The fishless cycling guide walks through that test.

Moving the first fish in is quicker. The Merck Veterinary Manual suggests floating the bag for about 20–30 minutes to match temperature, and gives 1 °F or °C per hour as the maximum safe rate of temperature change. A drip method, described by Chewy, takes 30–90 minutes.

What routine keeps aquarium water stable once fish are in?

A routine of regular partial water changes and testing keeps aquarium water stable, because nitrate keeps building between changes even in a fully cycled tank. Published schedules differ slightly. Practical Fishkeeping suggests about 25 % weekly, while the Merck Veterinary Manual's schedule changes water every 2 weeks (interval), with the amount set by how heavily the tank is stocked.

The nitrate level that should trigger more changes also varies by source. Aquarium Co-Op calls nitrate under 40 ppm safe, and Practical Fishkeeping uses the same figure above the level in your tap water, while Merck's freshwater reference value is stricter, at 20 mg/L (freshwater reference range, less than). Sensitive species and shrimp tanks are safer at the lower figure.

The maintenance guide sets these into a weekly and monthly plan, and the aquarium test kit comparison covers the kits used to read nitrate.

Does clear water mean an aquarium is safe?

No. Clear water says nothing about whether an aquarium is safe, because the most dangerous compounds in a new tank are invisible. This is the misconception behind many early fish deaths.

The Merck Veterinary Manual and Practical Fishkeeping both note that ammonia and nitrite are colourless, so a tank can look spotless while poisoning its fish; a test kit is the only way to confirm. Chlorine is just as invisible, and Merck reports fish deaths at 0.04 mg/L chlorine. The reverse is also true: a cloudy bacterial bloom in a cycling tank often looks alarming but is a water-quality signal rather than proof of danger.

The habit that replaces the myth is simple: test ammonia, nitrite and nitrate on a schedule, and test again whenever fish behave differently. The new tank syndrome guide lists the signs that a new tank's water is harming fish.

Which guides cover planted tanks and shrimp tanks?

Five guides cover planted tanks and shrimp tanks, which need more control over light, carbon dioxide and dissolved minerals than a basic fish tank.

Planted tanks

Start with the planted tank setup steps, then decide between a low-tech and a high-tech tank. Aquarium Co-Op describes low-tech as low light, no added CO₂ and light fertilising, and lists 10–20 PAR as low light, against 40–50+ PAR for demanding carpet plants. The low-tech planted tank guide covers the easier route. Tropica suggests a photoperiod of 8–10 hours/day once plants settle in. The CO₂ guide then explains why targets for high-tech tanks sit close to the level Merck warns can harm fish.

Shrimp tanks

Shrimp keepers track total dissolved solids (TDS), the combined minerals in the water. SaltyShrimp targets 100–150 ppm for Caridina bee shrimp and 200–250 ppm for Neocaridina such as cherry shrimp. Reaching the lower figure usually needs reverse osmosis (RO) water, which Green Aqua describes as 5–10 ppm before minerals are added back. The RO and DI water guide covers remineralising it, and notes from Michigan State University Extension that an RO unit can send 50–90 % of incoming water down the drain.

When do general water guidelines fail a particular species?

General water guidelines fail whenever a species sits at the edge of, or outside, the broad band they describe. A general figure is a starting point for fish as a whole, not a target for your fish.

pH is the clearest example. SRAC and Merck recommend 6.5–9.0 pH for freshwater fish in general, yet the Kuhli Loach is listed at pH 3.5–7.0 and the Cardinal Tetra at pH 4.0–7.5, both reaching well below that band. Temperature works the same way: the hobby tropical range of 75–80 °F is too warm for goldfish and the lower end is too cool for discus.

Nitrate shows how guidance itself changes over time. UF/IFAS notes an older view that freshwater fish tolerate around 200 mg/L nitrate (traditional view), alongside newer concern about long-term exposure, while Merck's aquarium reference is far lower. When a general guide and a species range disagree, the species range wins, and the species care data lists each one with its sources.