How to Cycle a Freshwater Aquarium Without Losing Fish
A step-by-step walkthrough of the nitrogen cycle, fishless and fish-in methods, and how to read test results to know when a tank is ready.
Freshwater Aquarium Reference
Tank cycling, water chemistry, and fish that get along.
Guides written for people setting up their first tank and for those moving past the basics — covering nitrogen cycles, pH and hardness, rooted and floating plants, and which species share a tank without issue.
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Topics
Four areas covered in depth
Each topic builds on the previous — start with cycling, then dial in water chemistry, add plants, and finish with fish selection.
Tank Cycling
How beneficial bacteria colonise filter media and convert ammonia into nitrite, then nitrate. Timelines, methods, and common failure points.
Water Parameters
pH, general hardness, KH, ammonia, nitrite, nitrate, and temperature ranges — what each value means and how to adjust it safely.
Plant Selection
Low-tech plants that root into substrate or attach to hardscape, floating species for surface cover, and CO₂ requirements for each growth type.
Species Compatibility
Which small schooling fish, dwarf cichlids, livebearers, and bottom-feeders share water chemistry requirements and temperament.
Substrate & Hardscape
Inert gravel versus nutrient-rich soil, buffering capacity of rocks and wood, and how hardscape choices affect water chemistry long-term.
Maintenance Schedules
Weekly water-change volumes, filter cleaning intervals, glass algae removal, and seasonal temperature adjustments for Polish tap water.
Latest articles
Recent guides
Choosing Aquarium Plants When You Are Just Starting Out
Java fern, Anubias, Amazon sword, and hornwort — which species survive without CO₂ injection, which need nutrients in the substrate, and how to attach rhizome plants correctly.
Compatible Freshwater Fish for Community Tanks
A practical look at which small tetras, rasboras, corydoras, and livebearers share overlapping water parameter requirements and coexist without aggression.
Get in touch
Questions about your tank?
Use the form to send a question or describe your setup. Replies go out within two business days. For urgent issues, use the phone number below.
Email: contact@underleycorner.eu
Phone: +48 22 333 44 55
Address: ul. Marszałkowska 84/92, 00-514 Warszawa, Poland
Company: UnderleyCorner Sp. z o.o. · NIP: PL5213012345 · REGON: 012345678