Why your angelfish ate your neons
Angelfish are cichlids. Neon tetras fit in their mouths. The only question is when, not if. How predation thresholds work and which tankmates survive.
Aquariums
Freshwater fishkeeping, planted tanks, and the gear that keeps them alive.
Start here
If you're setting up your first freshwater tank, read this first. The mistakes that kill beginner tanks aren't subtle: too small, not cycled, wrong fish for the size. The site has tools that solve each piece if you go in the right order.
1. Pick a tank size, not a fish
Counter-intuitive, but right. Bigger tanks are more forgiving because water chemistry shifts more slowly. A 75 L tank is easier to keep than a 20 L tank. Use the tank volume calculator to convert dimensions if you're buying secondhand or building. Skip nano tanks (under 40 L) on a first build; they punish small mistakes.
2. Cycle the tank before adding fish
This is the step beginners skip. The nitrogen cycle takes 4-6 weeks: bacteria colonies need to grow before they can convert fish waste safely. Read the nitrogen cycle guide for what's happening and how to feed the cycle with ammonia (the fishless method). Don't trust "cycle in a week" products on the shelf.
3. Pick fish that fit the tank, not the other way around
Use the stocking calculator to pick a roster the tank can actually support. The catalog has 128 species with real schooling minimums, adult sizes, and compatibility data. Common mistakes: putting six fish that each "need" 75 L into a 75 L tank, or one fish that schools in groups of 10+.
4. Substrate and plants, if you want them
A planted tank is harder than a fish-only tank but more rewarding. Use the planted tank planner to pick plants that share substrate, light, and water-parameter needs. The aquarium substrate reference explains what each substrate does to pH and plant nutrition.
5. Heater, filter, lighting
The heater wattage calculator tells you what size heater the tank needs for the temperature delta. Aim for slightly oversized; an undersized heater runs continuously and burns out. The aquarium lighting calculator helps you match fixture PAR to plant needs.
6. Water changes and monitoring
Test water weekly for the first three months. Ammonia and nitrite should read zero once cycled; nitrate climbs and gets diluted by water changes. The water change calculator tells you how much to swap based on current nitrate.
If a parameter is off, don't dose chemicals to fix it; usually the right answer is a partial water change. Chemistry shortcuts often make things worse.
Tools
Tank volume
Rectangular, bowfront, cylindrical, hex, and custom shapes. Reports gallons (US and imperial) and liters.
Fish stocking calculator
Bioload, schooling minimums, and weekly water change estimates. Replacement for the ancient AqAdvisor.
Water change
How much water to swap to bring nitrate, TDS, or any dilutable parameter down to a target value.
Heater wattage
How many watts of heating you need. Quick rule-of-thumb mode or physics-based detailed mode for non-standard tanks and unusual rooms.
Substrate volume
Substrate volume for a tank footprint plus depth. Estimates bag counts for common aquasoil, sand, and gravel products.
Tank weight calculator
Total weight on your floor: water, glass, substrate, hardscape, and stand. For anyone worried about putting a tank upstairs.
Medication dosing
Calculate the right dose for common aquarium medications, with species warnings based on your stocking.
GH / KH remineralizer
How much remineralizer to add to RO or distilled water to hit a target GH (and KH if the product raises both).
Nutrient dosing
EI, EI-lite, PPS-Pro, and commercial liquid dosing for planted tanks. Reads your saved plant roster to suggest a method.
CO2 / pH / KH calculator
Estimate dissolved CO2 in your planted tank from pH and KH readings.
Aquarium lighting
PAR-at-substrate targets by plant tier. Enter your fixture PAR-at-surface and tank depth, see which plants will thrive.
Planted tank planner
Pick the plants you want to keep, get a substrate recommendation, water parameter range, light and CO2 requirements, and fish-compatibility warnings.
Reference
Articles
The actual cost of keeping a fish tank for a year
A 200-liter community tank costs $150-250 per year to run after the initial setup. Electricity is the biggest line item. Here's the full breakdown by tank size.
Aquarium stand options and what matters
Weight capacity, leveling, and moisture resistance matter more than looks. How to evaluate commercial stands, DIY builds, and repurposed furniture.
Biotope aquariums: matching fish to their natural habitat
A biotope tank recreates a specific wild habitat with regionally accurate fish, plants, substrate, and water chemistry. Three setups worth trying.
Blackwater tanks: replicating acidic jungle streams
Blackwater setups use tannins from leaves and wood to create tea-stained, acidic water. Which botanicals to use, target parameters, and species that thrive in them.
Setting up a breeding tank
A dedicated breeding setup needs the right size, filtration, spawning triggers, and fry food. What to prepare for livebearers, egg scatterers, and cave spawners.
Canister vs HOB vs sponge filters
Three filter types, three different jobs. Canister for large tanks and heavy bioload, HOB for convenience, sponge for breeding and small setups.
Carpeting plants that don't need CO2
Monte Carlo, Marsilea, dwarf hairgrass, and dwarf sag can carpet without CO2 injection. Expect 8-16 weeks and proper light. Realistic timelines inside.
Driftwood in aquariums
Which wood types are safe for aquariums, how to stop them floating, how long tannins last, and whether to soak or boil. Practical prep and placement.
Dry fertilizers vs liquid: cost over a year
Liquid fertilizers cost 10-20x more per dose than mixing your own from dry salts. The math, the tradeoffs, and whether the convenience is worth it.
Understanding filter media
Mechanical, biological, and chemical filter media do different jobs. What each type does, the order they go in, and when (or if) to replace them.
Fish that recognize their owners
Oscars sulk when ignored. Bettas follow fingers. Puffers watch you eat dinner. The three-second memory myth is long dead, and some fish are paying more attention than you think.
Can my floor hold a fish tank?
A 200L tank weighs about 250 kg when filled. Most residential floors handle that fine, but apartment buildings, old houses, and upper stories have real limits. Here's how to check.
GH and KH explained without the chemistry degree
GH is dissolved minerals. KH is buffering capacity. One affects what fish you can keep, the other determines whether your pH stays stable overnight.
Glass vs acrylic tanks
Glass is heavier, cheaper, and scratch-proof. Acrylic is lighter, clearer, and fragile to algae scrapers. Which matters depends on tank size and where it's going.
Hardscape placement: rocks and wood that don't look random
The rule of thirds, odd-number groupings, and visual weight. Practical techniques for arranging rocks and driftwood so the layout looks intentional.
How bioload actually works
The math behind stocking calculators, why a pleco and six neons are not the same thing, and what the one-inch-per-gallon rule gets wrong.
Ich treatment ranked by effectiveness
Heat alone is unreliable. Salt helps but isn't enough. Malachite green and formalin have the best research behind them. What works, what doesn't, and what kills scaleless fish.
LED spectrum: what plants use vs what looks good
PAR, PUR, Kelvin, and why a bright-looking light can still grow algae instead of plants. How to read an LED spectrum chart and pick a light that does both jobs.
Live food cultures for aquarium fish
Baby brine shrimp, daphnia, microworms, and vinegar eels are easy to culture at home. Setup costs under $20 each. Here's how to start and maintain them.
Low-tech planted tank from scratch
No CO2 injection, no high-end lighting, no daily dosing. A planted tank with easy species, a standard light, and root tabs costs about the same as an unplanted setup.
Medicating a tank with snails and shrimp
Most fish medications kill invertebrates. Copper is always lethal to shrimp. Here's what's safe, what's not, and when to move animals instead of treating in place.
Moving an aquarium without disaster
How to drain, transport, and re-establish a fish tank during a move. Save filter media, keep substrate damp, and get everything running again in hours.
Old tank syndrome
What happens when you stop doing water changes for months. The fish adapt slowly to worsening conditions until a new addition dies overnight and you realize the water has been toxic for weeks.
Why your pH keeps crashing overnight
pH drops overnight because CO2 builds up while plants sleep and KH can't buffer the shift. Three causes, one fix.
Choosing substrate for a planted tank
Aquasoil, sand, gravel, and dirted (Walstad) tanks. What each does for plant growth, how long it lasts, and which one you'll regret least in two years.
Quarantine setup for $15
A plastic tub, a sponge filter, and a heater you already own. Quarantine doesn't require a second tank, and skipping it costs more than setting it up.
Why your red plants won't turn red
Red aquarium plants need high light, CO2, and controlled nitrate to produce anthocyanin pigments. Iron alone won't do it. Here's the actual science.
Using RO water in a freshwater tank
How to remineralize reverse osmosis water for aquarium use. Mixing ratios, GH and KH targets, common mistakes that crash parameters.
The schooling number matters more than you think
Three neon tetras isn't a school. Six is the minimum. Some species need 10 or more. Understocked schools produce stressed, aggressive, sick fish.
Keeping shrimp with fish: what actually works
Most fish eat shrimp if they can catch them. Some species reliably ignore them. The difference between a thriving colony and an expensive snack depends on fish choice, cover, and tank setup.
What substrate does to your water chemistry
Inert substrates leave water parameters alone. Buffering substrates change them on purpose. Knowing which you have prevents months of confusion.
Keeping your tank alive on vacation
A healthy tank runs itself for two weeks without intervention. Pre-trip prep, auto feeder settings, and what actually goes wrong while you're away.
Tap water varies more than you think
Your tap water parameters change with the seasons, after storms, and when the utility switches disinfection methods. How to test for it and what to do about it.
How water temperature affects fish metabolism
Fish are ectotherms. A 10 C rise roughly doubles their metabolic rate, oxygen demand, and feeding needs. What this means for your tank's real-world management.
A realistic weekly maintenance routine
What actually needs doing each week, what can wait, and how long it takes. A maintenance routine for a community tank takes 20-30 minutes, not the afternoon some guides imply.
Algae: what kind you have and how to fix it
Identification guide for common aquarium algae with actual causes and real fixes, not product recommendations.
Choosing a heater: wattage, placement, and when two are better than one
How to size a heater for your tank, where to put it, and why splitting the wattage across two heaters is safer than using one.
CO2 injection for planted tanks: what it costs, what it does, and when to skip it
Pressurized vs DIY, diffuser options, the pH swing issue, and a realistic look at which plants need CO2 and which grow fine without it.
How to cycle a fish tank
Fishless cycling from start to finish, plus fish-in cycling when you have no choice. Ammonia targets, phase timelines, how to speed it up, and troubleshooting a stalled cycle.
Medication dosing for common fish diseases
Ich, fin rot, columnaris, velvet, dropsy, fungal infections, and internal parasites. How to identify each, dose for your actual tank volume, set up a hospital tank, and what not to mix.
The nitrogen cycle explained
Ammonia turns into nitrite turns into nitrate. Here's what's actually happening in your filter and why it matters.
Stocking ideas by tank size
Concrete fish rosters for 40L, 75L, 120L, 200L, and 400L tanks. Each roster links to the stocking calculator pre-loaded and ready to adjust.
Water chemistry for fishkeepers: pH, GH, KH, and what they mean
What pH, GH, KH, and TDS measure, how they interact, the ammonia-pH toxicity relationship, chlorine vs chloramine in tap water, and when to adjust vs leave your water alone.