Fish aquarium accessories fall into two categories: things your fish genuinely need to survive, and things that make the tank look better or make maintenance easier. The must-haves are a filter, a heater (for tropical species), a thermometer, a light, a water conditioner, and some form of substrate or hiding spots. Everything else builds on that foundation.
The number of aquarium accessories on the market can feel overwhelming, especially when you're setting up your first tank. I've found that most beginners overbuy on decoration and underbuy on filtration. This guide covers the accessories that actually matter, explains what each one does, and gives you specific product names so you know what to look for. I'll also flag a few things that are popular but not particularly necessary.
Filtration: The Most Important Accessory in Your Tank
Your filter does three jobs: mechanical filtration (removing particles from the water), biological filtration (housing beneficial bacteria that process ammonia), and sometimes chemical filtration (removing dissolved compounds through activated carbon or other media). No other accessory compensates for poor filtration.
Hang-On-Back Filters
HOB filters are the most beginner-friendly option. The Aqueon QuietFlow 30 handles tanks up to 30 gallons and has a self-priming pump. The Marineland Penguin 350 is a step up for 50 to 75-gallon tanks and uses a bio-wheel for enhanced biological filtration.
Size your filter by gallons per hour (GPH) of flow rate. Aim for a filter that turns your tank volume over 4 to 6 times per hour. For a 40-gallon tank, that means a filter with at least 160 GPH, preferably 240 GPH.
Canister Filters
Canisters sit outside the tank and offer more media capacity than HOBs. They're quieter and more powerful, but require more maintenance effort. The Fluval 207 works well on tanks up to 45 gallons. The Fluval 307 handles up to 70 gallons. Sunsun and Aquatop offer more affordable alternatives in the $60 to $90 range.
For a broader look at filtration options, our best freshwater aquarium accessories guide covers current top-rated filters at each price point.
Heaters and Thermometers
Most tropical fish need water temperatures between 74 and 82 degrees Fahrenheit. A quality heater keeps that range stable.
The Eheim Jager 100W and the Fluval E-Series are two of the most reliable heater brands. The Eheim Jager has a glass tube design and auto-shutoff when exposed to air. The Fluval E200 has a dual display showing both target and actual temperature, which is a genuinely useful feature.
Heater wattage guidelines: roughly 3 to 5 watts per gallon of water. A 20-gallon tank needs a 50 to 75-watt heater. A 55-gallon tank needs 150 to 200 watts, and using two smaller heaters (like two 100-watt units) provides redundancy in case one fails.
Always verify your heater with a separate thermometer. Heater thermostats can drift over time. A $5 digital thermometer placed on the opposite side of the tank from the heater gives you an accurate reading of actual water temperature.
Lighting
Fish don't have the same demanding light requirements as corals, but they still need a consistent day/night cycle of 8 to 12 hours of light per day. Light also matters for planted tanks, where PAR (photosynthetically active radiation) values determine whether plants can photosynthesize effectively.
For a basic fish-only tank, the Aqueon Aquarium Light Hood or any LED strip in the 5,000 to 7,000 Kelvin color temperature range provides adequate lighting. These typically cost $20 to $45 depending on tank length.
For planted tanks, the Fluval Plant 3.0, the Finnex Planted+ 24/7, and the Chihiros WRGB series are all popular. The Fluval Plant 3.0 has a programmable app and covers the full spectrum plants need. Expect to pay $80 to $150 for a quality planted tank light.
For reef tanks, lighting requirements are far more demanding and expensive, typically starting at $200 and going well above $1,000 for larger systems.
Substrate and Hardscape
Substrate serves both aesthetic and functional purposes. In planted tanks, a nutrient-rich substrate like Fluval Stratum or ADA Amazonia gives plant roots the minerals they need. For fish-only tanks, standard aquarium gravel, sand, or bare bottom all work fine.
Hiding spots matter more than most new hobbyists realize. Fish under stress hide. A tank with no cover produces chronically stressed fish, which leads to disease and aggression. Simple options include:
- PVC pipe cut to size (cheap and inert)
- Terracotta flower pots laid on their sides
- Driftwood from an aquarium store (pre-soaked to remove tannins)
- Rock formations using slate or lava rock
Aquarium-safe decorations labeled as such are fine too. Just rinse them before adding them to the tank.
Air Pumps and Airstones
Air pumps push air through airstones to create bubbles. The bubbles don't directly add oxygen to the water. What they actually do is increase surface agitation, which improves gas exchange at the water's surface. This matters most in warm tanks, heavily stocked tanks, or during summer when dissolved oxygen levels drop.
The Tetra Whisper 60 is a quiet, reliable air pump for tanks up to 60 gallons. The Fluval Q2 is quieter still and handles up to 100 gallons. Both run on standard airline tubing connected to airstones.
Not every tank needs an air pump if the filter return creates enough surface movement. But in a 75-gallon tank with 30 fish and a summer temperature of 82 degrees, adding an airstone at night can be the difference between your fish gasping in the morning and swimming normally.
Water Testing and Conditioning Supplies
These aren't glamorous, but they matter more than most decorative accessories.
Seachem Prime is the water conditioner I mentioned in our cleaning supplies guide. It's the same product here because it's just that good. API Master Test Kit (freshwater or saltwater depending on your setup) covers the four parameters you need to track: ammonia, nitrite, nitrate, and pH.
Check our buy aquarium accessories online guide if you want to compare prices across suppliers and find the best deals on these essentials.
Optional Accessories Worth Considering
Once your tank is established and stable, these additions genuinely improve the experience:
Auto top-off (ATO) units: Water evaporates and concentrated saltwater or unbalanced freshwater causes parameter drift. An ATO like the Innovative Marine HYDROFILL refills the tank automatically from a reservoir. Worth every penny in a reef setup.
Timer strips: Plug your lights into a digital timer to automate your photoperiod. Consistency in lighting reduces fish stress. Any basic digital outlet timer works. You don't need a smart plug for this.
Surface skimmer attachment: If you have a canister filter, adding a surface skimmer intake removes the protein film that forms on the water surface. Fluval and Eheim both make these.
FAQ
Do I need all these accessories right away? No. The absolute minimum is a filter, a heater (for tropical fish), a thermometer, a light, and a water conditioner. You can add the rest over time as you learn what your specific fish and tank need.
What's the most common mistake when buying aquarium accessories? Undersizing the filter. A filter rated for "up to 20 gallons" is often marginal on a fully stocked 20-gallon tank. Buying one size up almost always pays off.
Can I use decorations from outside, like rocks from a river? Only after testing them. Place suspected rock in white vinegar. If it bubbles, it contains calcium carbonate, which can affect your pH. River rocks are often fine but should be boiled and tested before use. Avoid painted rocks and any porous material that might have been exposed to chemicals.
How long do aquarium accessories typically last? Heaters last two to five years before their thermostat becomes unreliable. Filters last much longer, often eight to ten years with impeller replacements. LED lights typically last 30,000 to 50,000 hours. Plan to replace heaters proactively every three years in critical setups like reef tanks.
Build Your Accessory Kit in Order
Start with the non-negotiables: filter, heater, thermometer, light, and water conditioner. Once the tank is running and stable, add testing supplies and any species-specific needs. Decoration and convenience accessories come last. That ordering saves money and prevents the mistake of buying attractive equipment that doesn't actually support your fish.