Guide
Aquarium keeping in the USA
US gallons, tap water by region, retail, and what American hobbyists need to know.
- Use US gallons everywhere: Tank sizing, dosing instructions, stocking rules, and heater/filter specs are all labelled in US gallons (1 US gal = 3.78 L) by every major American brand.
- Test your tap before buying fish: Water hardness and pH vary dramatically by region - matching fish to your actual water beats trying to constantly correct it with chemicals.
- Cycle before you stock: The nitrogen cycle takes 4-8 weeks. Skipping it is the single biggest cause of new-tank fish deaths in the US hobby.
- Local fish stores beat chains for advice and livestock: Petco and PetSmart are fine for equipment and basics; your local fish store (LFS) is where you find healthier, better-acclimated fish and honest guidance.
- Know the Lacey Act and your state rules: Certain species are federally or state-restricted. Buying or transporting them across state lines is a federal offense - and releasing any aquarium species into the wild is both illegal and ecologically destructive.
US gallons: why the unit matters more than you think
Every dosing instruction, stocking guideline, filter flow rate, and heater wattage recommendation you'll encounter in the American hobby is calibrated to US gallons. That sounds obvious until you're reading a UK fishkeeping forum or using a European brand that labels in litres or imperial gallons - at which point a dosing error is easy to make.
One US gallon is 3.785 litres, or about 0.833 imperial gallons. The difference between US and imperial gallons is roughly 20%, which matters when you're dosing medications like API General Cure or Seachem Metro. Always check which gallon a product is referencing. Every major US brand - API, Seachem, Aqueon, Tetra, Fritz - uses US gallons on the label, so if you're buying domestic products and using domestic stocking guides, you're consistent. Problems arise when you mix sources.
If you're unsure of your tank's actual volume (glass thickness and internal equipment reduce it), fill it with a measured container before you ever dose medication. A 55-gallon tank with a large sump and thick substrate might hold closer to 45 gallons of actual water.
Tank sizes in the US are somewhat standardized: 10, 20 (long or high), 29, 40 breeder, 55, 75, 90, 125 gallons are the most common footprints. The 40-breeder (36" × 18" × 16") is widely considered one of the best all-around tanks in the hobby - wide footprint, manageable water volume, and readily available at most stores.
Tap water across the US: what you're actually working with
This is where a huge portion of American fishkeepers go wrong. They buy fish based on what looks good at the store, then spend months fighting parameters that don't suit those fish - when the real fix was choosing fish that match their tap water from the start.
Regional hardness and pH patterns
The US has dramatic regional variation in tap water chemistry, and it tracks geology closely:
- Great Plains and Midwest (Texas, Kansas, Ohio, Illinois): Typically hard, alkaline water. GH often 15-25 dGH, pH 7.5-8.4. Excellent for African cichlids, livebearers like guppies and mollies, and hard-water tetras. Challenging for soft-water species like discus or wild-type cardinal tetras.
- Northeast (New England, upstate New York): Variable - some areas pull from soft mountain reservoirs (pH 6.8-7.2, GH 3-8 dGH), others from limestone-heavy aquifers. Test yours specifically.
- Pacific Northwest (Oregon, Washington): Generally soft, slightly acidic water from snowmelt-fed reservoirs. GH often 1-5 dGH, pH 6.5-7.2. Great for South American species, planted tanks, and soft-water Corydoras.
- Southeast (Florida, Georgia, coastal Carolinas): Mixed. Florida's water is notoriously hard and alkaline in many municipalities due to limestone geology. Coastal areas often add chloramines rather than chlorine - relevant for dechlorinator choice.
- Southwest (Arizona, Nevada, Southern California): Very hard, alkaline, often with elevated TDS from mineral-rich groundwater. pH 7.8-8.6 is common. Livebearers thrive; soft-water fish struggle without RO water.
Many US municipalities use chloramines instead of chlorine - especially in the South and coastal cities. Standard sodium thiosulfate dechlorinators don't neutralize chloramines. Use a product that explicitly states it handles chloramines: Seachem Prime, API Tap Water Conditioner, or Fritz Complete all work. Check your local water utility's annual Consumer Confidence Report (it's public and free) to know exactly what's in your tap.
Well water
Rural households across the US often rely on well water. Well water bypasses municipal treatment, which means no chlorine or chloramines - but it can contain elevated nitrates, hydrogen sulfide, iron, or other metals that are harmful to fish. If you're on well water, test for nitrates and heavy metals before using it, and aerate it for 24 hours before adding it to a tank to off-gas any dissolved gases.
Most US fishkeeping guides tell you to "just match your water parameters to the fish." That's correct, but backwards in practice. A beginner should look up their municipal water report first, then browse fish that suit those parameters - not fall in love with a fish and then try to engineer their water to match. Chasing chemistry is an advanced skill and an ongoing maintenance burden.
Where to buy: chains, local stores, and online
The US retail landscape for aquarium keeping is more varied than most other countries. You have three real channels, and each has genuine strengths.
Petco and PetSmart
Both chains stock a reasonable range of tanks, filters, heaters, and basic dry goods. API test kits, Seachem products, Aqueon equipment - you'll find them at either store. Fish quality varies enormously by location and by which staff member ordered the livestock that week. Some locations are excellent; others hold fish in overcrowded, undertreated systems. Always look at the tanks before buying: if multiple fish are showing disease signs or there are dead fish in the tank, pass.
PetSmart runs Petco's main competition and the two are broadly similar in selection. Both occasionally run dollar-per-gallon tank sales (Petco more reliably), which are genuinely good deals for standard glass tanks.
Local fish stores (LFS)
A good LFS is worth the extra drive and the slightly higher price. Staff at independent stores tend to keep fish themselves, quarantine livestock properly, and carry species you won't find at chains - wild-caught Apistogramma, specialty plecos, interesting rasboras, tissue-culture aquatic plants. They're also far more likely to talk you out of a bad purchase, which saves money and fish lives.
Find your nearest LFS through the Fish Store Locator or aquarium club forums. Clubs like the American Cichlid Association (ACA) or your regional aquarium society also run auctions where you can source fish and plants from fellow hobbyists for low prices.
Online retailers
LiveAquaria, Aquatic Arts, and several specialty breeders on Aquabid or Aquarium Co-Op's store ship fish directly. Quality from reputable online sellers is often higher than chain stores because they specialize. Shipping stress is real, though - fish need a proper acclimation period after arrival, and orders placed in extreme heat or cold add risk.
Making it the second most popular pet category in the country after dogs and cats, according to APPA survey data.
The nitrogen cycle: don't skip this
The single most preventable cause of fish death in newly set-up US tanks is adding fish before the tank has cycled. A cycled tank has an established colony of beneficial bacteria (Nitrosomonas and Nitrospira spp.) that convert toxic ammonia from fish waste into nitrite, then into the far less toxic nitrate.
This process takes 4-8 weeks in a new tank using the fishless cycling method - longer if you're using a fish-in cycle. Ammonia spikes above 0.5 ppm cause gill damage and stress. Nitrite above 0.5 ppm is toxic. Neither is visible to the eye; you need a test kit. The API Freshwater Master Test Kit is the standard in the US hobby and costs around $25-35 at most stores.
For a full walkthrough, see the guide on how to cycle a fish tank. If you want to understand what's actually happening chemically, the nitrogen cycle explained covers the biology in detail.
Most beginners dose too much ammonia during a fishless cycle, then can't get it to drop. For a 20-40 gallon tank, you only need ammonia to read 2-4 ppm to feed the bacterial colony. Going to 8 ppm doesn't speed anything up - it creates a backlog that stalls the cycle for weeks.
US brands worth knowing
American fishkeepers have access to some of the strongest product lines in the hobby. Here's what actually gets used:
- API: Test kits (the Master Kit is the hobby standard), Stress Coat, Melafix, General Cure. Widely available, good value.
- Seachem: Prime (best all-around dechlorinator/detoxifier), Flourish line for planted tanks, Stability for bacterial colonization, Paraguard for disease treatment. Premium price, but Prime is worth every cent.
- Aqueon: Budget-friendly tanks, heaters, and filters. Their QuietFlow filters are solid starter units. Owned by Central Garden & Pet.
- Fritz Aquatics: Fritz Complete (dechlorinator), Fritz Zyme 7 (bacterial supplement for cycling). Increasingly popular as an alternative to Seachem.
- Fluval: Canadian brand but widely available in the US. Their FX and 07 series canister filters are some of the best on the market at their price points.
- Aquarium Co-Op: A YouTube-based brand out of Washington state that makes genuinely good products (sponge filters, Easy Green fertilizer, test strips) with honest, hobbyist-first marketing.
The Lacey Act and invasive species laws
The US takes aquatic invasive species seriously, and the legal framework around it is more complex than most hobbyists realize.
The Lacey Act
The Lacey Act (16 U.S.C. §§ 3371-3378) prohibits the import, export, transport, sale, and purchase of fish, wildlife, and plants taken or traded in violation of US or foreign law. For aquarium keepers, the most relevant application is the Injurious Wildlife List (maintained under the Act), which bans interstate transport of listed species including several snakehead species (Channa spp.), bighead and silver carp, certain walking catfish (Clarias spp.), and aquatic plants like water hyacinth and giant salvinia. Violations carry civil penalties up to $10,000 and criminal penalties for knowing violations.
State-level restrictions
State laws vary considerably and in some cases are stricter than federal rules. California, for example, prohibits a long list of species including piranhas, most turtles, and several catfish species. Florida restricts lionfish, certain cichlids, and numerous other species due to their release history in Florida waterways. Always check your state fish and wildlife agency's website before purchasing an unfamiliar species.
Never release aquarium fish, plants, or invertebrates into any natural waterway, storm drain, or outdoor pond connected to the wild. Goldfish, red-eared sliders, and common pleco (Pterygoplichthys spp.) populations have established in Florida, Texas, and California waterways through exactly this kind of release. The ecological damage is significant and permanent. If you can't keep a fish, rehome it through a club, give it back to your LFS, or contact your state wildlife agency for options.
What this means practically
Before you order anything unusual online or across state lines, spend five minutes checking the US Fish and Wildlife Service's injurious wildlife list and your state agency's prohibited species list. Reputable online retailers won't ship restricted species to states where they're banned - but not all sellers are reputable.
Practical tips specific to the US hobby
- Dollar-per-gallon sales: Petco runs these periodically (usually spring and fall). Buy extra tanks when they come up - a 10-gallon quarantine tank for $10 is a bargain you'll be glad you grabbed.
- Water change frequency: For most stocked community tanks, weekly 25-30% water changes are the standard. The guide on how often to do water changes covers when you can do less and when you need to do more.
- Stocking: The old "one inch per gallon" rule is outdated and misleading - a 10-inch common pleco in a 10-gallon tank is obviously wrong. Use a proper stocking calculator that accounts for bioload, territory, and swimming space.
- Aquarium clubs: Join one. The American Cichlid Association, North American Native Fishes Association (NANFA), and regional clubs run auctions, speakers, and plant swaps. You'll find species and expertise that no store can match.
- Logging parameters: Using App-aquatic to log your test results over time is genuinely useful - you'll catch slow parameter drifts and seasonal changes in tap water that you'd otherwise miss until something goes wrong.
Track your parameters and get care reminders with App-aquatic.
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