Setting up a fish tank means gathering quite a few accessories beyond just the tank itself. A fully equipped aquarium needs filtration, lighting, a heater, substrate, a water conditioner, a net, a gravel vacuum, and decorations at minimum. Some of those items are non-negotiable for keeping fish alive, while others improve the experience for both you and the fish.
This guide covers every category of fish tank accessory you'll encounter, explains what each one does, and helps you figure out which ones your setup actually needs. Whether you're building your first tank or upgrading an existing one, you'll leave with a clear picture of what to buy, what to skip, and what order to prioritize.
Life Support Accessories: The Non-Negotiables
These are the accessories your fish cannot live without. Skip any one of them and you'll have problems within days.
Filtration
A filter is the single most important accessory in any tank. It handles three types of filtration: mechanical (removing physical debris), biological (beneficial bacteria that process fish waste into less harmful compounds), and chemical (activated carbon removing odors and discoloration).
For tanks under 20 gallons, a hang-on-back filter like the AquaClear 20 or the Marineland Penguin 100B works well. Both run around $25 to $35 and are easy to maintain. For tanks 30 gallons and up, consider a canister filter like the Fluval 207 or the Eheim Classic 250, which offer more filtration capacity and keep the tank looking cleaner since all the equipment hides below.
The general rule is to filter your tank volume 5 to 10 times per hour. A 20-gallon tank needs a filter rated for 100 to 200 gallons per hour.
Heater
Most tropical fish need water between 74 and 80 degrees Fahrenheit. Without a heater, your tank temperature will follow room temperature, which causes stress and illness in fish.
A 5-watt-per-gallon heater is the standard recommendation. For a 20-gallon tank, that means a 100-watt heater. The Eheim Jager TruTemp and the Fluval E Series are both reliable options that hold temperature within 0.5 degrees of your target setting.
Air Pump or Surface Agitation
Fish need oxygen in the water. Filters that agitate the surface handle this in many setups, but if you run a sponge filter or have a heavily planted tank, a separate air pump like the Tetra Whisper AP or the Aquarium Technology ATMAN AT-A1500 can supplement oxygenation. These run between $10 and $20.
Water Quality Accessories
Water Conditioner
Tap water contains chlorine and chloramines that will kill the beneficial bacteria in your filter and irritate fish gills. You need a dechlorinator like Seachem Prime or API Stress Coat before every water change. Prime is particularly efficient: a single 500ml bottle treats about 5,000 gallons.
Test Kit
You can't manage what you don't measure. The API Freshwater Master Test Kit tests for ammonia, nitrite, nitrate, and pH, which are the four parameters that matter most. The kit costs around $25 and contains enough reagents for 800 tests. Liquid test kits are significantly more accurate than strip tests.
Water Bucket and Siphon
A dedicated 5-gallon bucket (never used for cleaning products) and a gravel siphon are how you do water changes. The Python No Spill Clean and Fill system connects directly to your faucet and simplifies the process for tanks over 30 gallons. For smaller tanks, a simple hand siphon like the Lee's Slim-Line gravel vacuum works fine.
Substrate and Decoration Accessories
Substrate
Gravel, sand, or bare bottom are the main choices. Gravel in the 2 to 5mm range works for most community tanks and is easy to vacuum. Carib Sea Eco-Complete provides a planted-tank substrate that also buffers pH. Pool filter sand (50 lb bags from hardware stores) is a budget option for fish that prefer sandy bottoms, like corydoras catfish.
Plan on 1 to 2 pounds of substrate per gallon for a shallow layer, or 2 to 3 pounds per gallon for plants.
Decorations and Hides
Fish need places to hide and feel secure, especially when they're new. Ceramic caves, driftwood, and rock formations all work. Live or artificial plants add cover and break up sightlines between aggressive fish. Silk plants are softer on fins than plastic and look more natural.
For a 20-gallon community tank, you might spend $30 to $60 total on decorations. Don't overfill the tank though since fish need open swimming space too.
Lighting
Most freshwater fish don't need specialized lighting. A basic LED hood light that came with your tank kit works for fish-only setups. If you want live plants, you'll need to step up to a light rated for planted tanks, like the Finnex Planted+ 24/7 or the Current USA Satellite Plus Pro.
Planted tank lights are measured in PAR (photosynthetically active radiation). For low-light plants like anubias and java fern, 20 to 40 PAR is enough. For carpeting plants, you need 40 to 80 PAR.
Maintenance Accessories
Algae Scrapers
Algae grows on tank glass within a few weeks in any lit tank. A magnetic algae scraper lets you clean the glass without putting your hand in the water. The Flipper Standard works well for standard glass, though for acrylic tanks you need a model with a soft pad to avoid scratching.
Aquarium Net
You'll use a net constantly: catching fish for transport, removing dead plant leaves, scooping out snails. Get two sizes, a small 4-inch fine-mesh net for small fish and a larger 6-inch net for scooping quickly.
Airline Tubing and Check Valves
If you run an air pump, you need silicone airline tubing to connect it to air stones or sponge filters. Plastic tubing gets stiff and cracks; silicone stays flexible. Add a check valve to prevent water from siphoning back into the pump if the power goes out.
You can find a complete breakdown of the most useful items in the Best Freshwater Aquarium Accessories guide, which covers specific product recommendations across each category.
Specialty Accessories Worth Considering
CO2 Systems
If you want a densely planted tank with fast-growing carpeting plants, a CO2 injection system makes a real difference. The Fluval Pressurized CO2 Kit 45g is a good entry-level option. More serious planted tank enthusiasts use paintball CO2 setups with a solenoid and drop checker.
Auto Top-Off
Water evaporates, and topping off daily is annoying. An auto top-off unit like the Tunze Osmolator 3155 keeps your water level constant by automatically adding fresh water as it evaporates. This matters most for saltwater tanks but also helps freshwater setups.
Fish Food and Feeding Accessories
A good variety of foods keeps fish healthy: flakes or pellets for staple feeding, frozen bloodworms or brine shrimp as treats. An automatic feeder like the Eheim Auto Feeder dispenses food on a schedule, which is useful for vacation coverage.
How to Budget Your Accessory List
For a basic 20-gallon freshwater community tank, here's a rough budget:
- Filter (AquaClear 30): $35
- Heater (Aqueon Pro 100W): $25
- Thermometer: $8
- Gravel vacuum (Lee's 9-inch): $10
- Water conditioner (Seachem Prime 500ml): $12
- Test kit (API Master Kit): $25
- Substrate (Carib Sea Medium Gravel 20 lb): $20
- Decorations and plants: $30 to $60
- Net: $5
- Algae scraper: $12
Total for essentials: roughly $180 to $215, not including the tank itself. For a more complete shopping reference with product comparisons, the Best Buy Aquarium Accessories Online guide covers where to get the best prices and what brands consistently perform.
FAQ
Do I need all of these accessories before I add fish? You need the filter, heater, dechlorinator, and test kit before fish go in. The filter needs to run for at least 2 to 4 weeks before adding fish to build up beneficial bacteria, a process called cycling. Decorations, plants, and a gravel vacuum can come before or after fish arrive.
What's the most common accessory mistake new fish keepers make? Buying a filter that's too small. People buy the filter rated "for up to 20 gallons" for their 20-gallon tank, but that rating is usually based on minimal stocking. Get a filter rated for at least 1.5 times your tank volume to have enough biological filtration capacity.
Can I skip the heater if my house stays warm? For tropical fish, probably not. Room temperature in most homes sits between 68 and 72 degrees Fahrenheit, which is below the 74 to 80 degree range most tropical fish need. Consistent temperature matters as much as the temperature itself; houses also get colder at night and in winter. A heater is inexpensive insurance.
How often do I need to replace aquarium accessories? Filter media (sponge, ceramic rings, bio balls) lasts years and should never all be replaced at once since it houses your beneficial bacteria. Carbon inserts lose effectiveness after 4 to 6 weeks. Heaters typically last 3 to 5 years. Replace bulbs in older fluorescent fixtures every 12 months even if they still light up, since light spectrum shifts and intensity drops before visible failure.