Freshwater aquariums, by the numbers
Know what your tank can handle before you add the fish.
Most fish losses in new tanks come from arithmetic nobody did: too little real water, too much bioload, ammonia nobody measured. Tank Math Lab gives you transparent calculators and careful guides so you can see the math, check it with a test kit, and decide for yourself.
Calculators
Stocking & Bioload Planner
Estimate net water volume, bioload and compatibility for a planned community, with every formula shown.
Fishless Cycle Ammonia Dosing Calculator
Work out how much household ammonia or ammonium chloride reaches your target ppm, with unit conversions.
New tank? Start here
Step 1 · Cycling
How to Fishless Cycle a Tank Using the 2 ppm Ammonia Method
A step-by-step fishless cycle: dose ammonia to about 2 ppm, track nitrite, avoid stalls, and confirm the tank clears ammonia in 24 hours before adding fish.
Step 2 · Stocking
How Many Fish Can a 20-Gallon Tank Hold? A Worked Approach
Stock a 20-gallon aquarium by real water volume, bioload and behavior, not inches. Covers 20 high vs 20 long, net gallons, and five example stocking plans.
Step 3 · Maintenance
Water Change Math: How Much and How Often to Control Nitrate
Derive the steady-state nitrate formula, size weekly water changes to stay under about 20 ppm, and account for nitrate already in your tap water.
Step 4 · Water Chemistry
Aquarium Test Kits Explained: Liquid, Strips and Digital Meters
What aquarium test kits really measure, why NH3 and NH3-N readings differ, accuracy traps in liquid kits and strips, and how to check a kit against a standard.
More guides
- Aquarium Filter Flow Rate: Rated vs Real Turnover Explained · Equipment
- What Size Aquarium Heater Do You Need? Watts, Delta-T and Safety · Equipment
- Fish-In Cycling: How to Protect Fish in an Uncycled Tank · Cycling
- GH, KH and pH Explained: Hardness, Buffering and Safe Changes · Water Chemistry
- Low-Tech Planted Tank Setup Without CO2: Plants, Light, Soil · Planted Tanks
- The Aquarium Nitrogen Cycle Explained: Ammonia to Nitrate · Cycling
What makes Tank Math Lab different
Formulas in the open. Every calculator explains exactly how it reaches its answer, including which parts are physics and which parts are rules of thumb. You can redo the math on paper.
Sources on every guide. We lean on university extension publications, species databases and manufacturers’ technical documents, and we link them so you can read the originals.
No invented experience. When a guide would benefit from our own measurements, it says so in a clearly marked “Field test pending” box until the data exists. Read more in our editorial policy or learn who runs the site.