Aquarium

Real volume, real stocking math.

Real volume, real stocking math.

Tank volume calculators that account for substrate and hardscape displacement. Stocking density math by species. Filter sizing for actual bioload, not what the box claims. For freshwater and saltwater hobbyists.

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Calculators

Working tools that answer one specific question. No "sign up to see results." No upsell paywall.

Most used Tank Volume Calculator Five tank shapes (rect, bowfront, cube, cylinder, hex). Subtracts substrate, hardscape, and water-line gap. Output: actual gallons your filter and heater need to handle. Open calculator → Stocking Density Pick species. Returns sustainable count per gallon, with adjustments for aggression and territory needs. Open calculator → Filter Flow Rate GPH needed for your bioload. Why the manufacturer ratings are 2x optimistic. Open calculator →

Real Gear Reviews

The cheap option is usually fine. When it isn't, this site says so. Reviews include real cost-of-ownership math, not "5 stars on Amazon" reasoning.

GuideYou're not keeping fish, you're keeping waterThe beginner buys a tank, fills it, and adds fish on day one. The fish die, and it feels like bad luck. It wasn't. The whole hobby is one idea the pet-shop c…GuideThe Aquarium Nitrogen Cycle: Why You Set Up Bacteria Before Fish (Fishless Cycling)Most new tanks fail for one reason: fish go in before the bacteria that keep them alive. The nitrogen cycle explained plainly, how to do a fishless cycle, an…

Why this page exists

Aquarium content online is mostly LFS upselling and YouTubers running $5000 dream tanks. This site is run by a person who has actually crashed a cycle.

The math here is for real home tanks with real water-change schedules and real budgets. The expensive equipment isn't always better; the calculators tell you when it actually is.

Plain note about money. Some links in the reviews and calculator results go to product pages on eBay with an affiliate tag. If you buy through one, the commission pays for the site. Your price doesn't change. The cheap option is usually fine; when the expensive option is worth it, this site will explain exactly why.

Guides

Gear actually worth buying

Smart eBay searches we'd start with ourselves. We earn a small commission on qualifying sales through these links; the price you pay is the same whether you use them or go direct to eBay. Full disclosure.

🔍 Shop Aquarium on eBay →
4.5 Gallon Ultra Clear Glass Aquarium,16 X 7.8 X 8.3", Rimless Fish Tank 6MMGlass aquarium tankeBay has a solid secondhand market for tanks. Check for scratches and check the seals before committing. Uimoso 100 Gallon 4 Stage Aquarium Canister Filter 9w UV 317GPH Fish Tank w/PumpCanister filterCanister filters (Fluval, Eheim, SunSun) outperform HOB filters for tanks 40 gallons and up. hygger Bright LED Aquarium Light Plants Grow Light Waterproof Fish Tank Clip-onFull-spectrum aquarium LED lightPlanted tanks need PAR, not just brightness. Fluval Plant 3.0 and Chihiros are the known-good options. Natural Aquarium Substrate Organic Gravel Aquascape Planting Eco Friendly NewAquarium substrate / gravelInert gravel is fine for fish-only. Planted tanks need nutrient-rich substrate (Fluval Stratum, ADA). Aquael Ultra Heater 150W Submersible Unbreakable Aquarium 2 in 1 ThermometerHeater + thermometerCobalt Aquatics and Eheim heaters hold temperature steadily. Avoid no-brand heaters — they cook fish.
Browse all Aquarium listings on eBay →

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