Most aquarium hobbyists underestimate what it actually costs to keep fish and plants alive month-to-month. Between water treatments, food, filter maintenance, and plant supplements, a modest 20-gallon tank can easily run $30–$80 monthly. Here's what you'll actually spend and where you can optimize your budget.
Food and Feeding
Fish food is your most predictable recurring expense. A small container of quality flake food for community tanks runs $5–$12 and lasts 4–8 weeks, depending on tank population and feeding frequency. Specialized diets cost more: sinking pellets for bottom feeders ($8–$15), spirulina-based foods for cichlids ($10–$18), and live or frozen foods like bloodworms or brine shrimp ($6–$14 per container) add up fast if you feed them regularly.
Budget $10–$25 monthly on food alone for a 20–40 gallon setup with 10–15 fish. Larger tanks or species with expensive dietary needs (marine fish, discus) can push this to $40–$60 monthly.
Water Treatments and Additives
Tap water isn't safe for fish straight from the tap. You'll need a dechlorinator every time you do water changes—typically $8–$15 per bottle, lasting 2–4 months depending on tank volume and change frequency.
If you're keeping live aquatic plants, add fertilizers to the list. Comprehensive liquid fertilizers run $10–$20 per bottle and last 4–8 weeks. Trace elements, macronutrients (nitrogen, phosphorus, potassium), and CO2 systems push costs higher for planted tanks.
For fish-only setups, plan $8–$15 monthly. Planted aquariums easily double this: $20–$40 per month.
Filter Media Replacement
Your filter is your tank's lifeline, and maintaining it properly prevents dead fish and costly mistakes.
- Mechanical media (foam, floss): $5–$12, replace monthly or every 4 weeks
- Biological media (ceramic rings, sponges): $8–$18, replace every 2–3 months
- Chemical media (activated carbon, resins): $6–$14, replace monthly if you're using it
- Complete filter cartridges: $12–$30 each, replace every 4–6 weeks
A single hang-on-back filter averages $15–$25 monthly in media costs. Canister filters are pricier up front but often cheaper long-term: $15–$35 monthly depending on filtration setup.
Substrate and Plant Maintenance
If you're growing live aquatic plants, substrate matters. Nutrient-rich plant substrates (like Aquasoil) don't need monthly purchases, but if you're using sand or gravel with root tabs, budget $10–$20 monthly for fertilizer pellets or liquid supplements.
Plan occasional plant trimming supplies: aquascaping scissors ($8–$15 one-time cost) and root stimulants ($12–$18 per bottle, lasting 2–3 months).
Electricity
Running an aquarium costs money you might not see on a receipt. A standard 20-gallon setup with LED lights, filter, and heater uses roughly $5–$12 monthly in electricity. Larger tanks (75+ gallons) with multiple devices run $15–$30 monthly. While not a direct product purchase, this is real spending to factor into your annual budget.
Unexpected Replacements
Equipment fails. Heaters burn out ($25–$60 replacement), lights dim ($30–$100), air pumps stop working ($15–$40). Set aside $5–$10 monthly as a buffer for replacements—over a year, this adds up to realistic maintenance fund.
Seasonal Considerations
Spring and summer often mean algae blooms, requiring extra water treatments ($8–$15). Winter heating costs spike in cold climates. Plan for $10–$20 extra in spring and winter months.
Smart Spending Tips
Buy filters and media in bulk when you find good prices. Compare suppliers on Mercoly to find trusted Live Fish & Aquatic Plants providers offering bulk discounts and consistent pricing. Subscribe to auto-shipments for routine items like food and dechlorinator—most suppliers offer 10–15% discounts. Generic food works fine for hardy fish; save specialty diets for sensitive species.
Frequently Asked Questions
Q: How often should I replace filter media in a planted tank versus a fish-only tank? Fish-only tanks need media replacement every 3–4 weeks; planted tanks can stretch to 6–8 weeks since plants help consume nitrates and reduce bioload.
Q: Do I really need fertilizers if I'm just keeping hardy fish and basic plants? Hardy plants like Anubias and Java Fern survive without added fertilizers in established tanks, but growth is noticeably slower—fertilizers cost $10–$20 monthly but produce healthier, faster-growing plants.
Q: Can I reduce monthly costs by doing less frequent water changes? No; skipping water changes means skipping dechlorinator and new beneficial bacteria, but it leads to algae blooms and sick fish that cost far more to treat or replace.
Start tracking your actual spending this month, then use that baseline to find deals on the supplies you use most.