AquaCompat
Free resources

Free Aquarium Illustrations (CC BY 4.0)

Every explanatory illustration on AquaCompat is free to reuse under the Creative Commons Attribution 4.0 licence (CC BY 4.0). The library covers the nitrogen cycle, water chemistry, tank setup, fish compatibility, fish health and equipment choices. Each diagram can be downloaded as an SVG and republished on a blog, in a newsletter, in teaching material or in a commercial product, provided you credit "Illustration: AquaCompat" with a link to that illustration on this page. Use the copy-credit button under any image to get the exact line.

By AquaCompat Editorial Team Updated How we research

What do the aquarium illustrations cover?

The illustrations are the diagrams drawn for AquaCompat's guides, so each one explains a single idea from the page it was made for. They fall into six main groups:

  • Water chemistry and the nitrogen cycle: where aquarium nitrogen goes, why a single zero reading does not prove a cycle, GH against KH, pH and buffering, tap water treatment, RO water and TDS in shrimp tanks.
  • Fish compatibility: how a compatibility verdict is made, why a hard failure overrides a score, and water-range and candidate-verdict charts for individual species such as angelfish, discus and cherry shrimp.
  • Tank setups: planning a 10-gallon community, giving plants and fish their own space in a planted tank, and the order to set up a new aquarium.
  • Fish health: the ich life cycle, fin rot, swim bladder signs, cloudy water, new tank syndrome, appetite loss and planaria compared with hydra.
  • Equipment: how a sponge filter works, sizing a heater, canister flow ratings, CO2 system parts, plant lighting and choosing a test kit or water conditioner.
  • Species comparisons: adult size and minimum tank side by side, for example Caridina against Neocaridina shrimp.

Below each image you will find its title, a link to the guide it appears in, the SVG download and the copy-credit button. The anchor of each illustration on this page is the address to use in your credit link.

Browse the illustrations

Credit line format: Illustration: <a href="https://aquacompat.com/image-library/#ID">AquaCompat</a> (CC BY 4.0)

What can you do with the illustrations?

Under CC BY 4.0 you may use, copy, adapt and republish any illustration in this library, including for commercial purposes, with no fee and no need to ask first. That covers blog posts, club newsletters, school worksheets, slide decks, social posts, printed handouts, product manuals and shop signage. You may recolour, crop, translate or relabel a diagram to fit your own material.

The one condition is attribution. Credit each illustration you use with the line below, linking "AquaCompat" to that illustration's anchor on this page, which the copy-credit button fills in for you:

Illustration: <a href="https://aquacompat.com/image-library/#learn--nitrogen-cycle">AquaCompat</a> (CC BY 4.0)

If you have changed the illustration, add "adapted" to the credit. In print, where a link cannot be clicked, write out the address in full. Please do not imply that AquaCompat endorses your product, site or publication.

Are the illustrations accurate enough to quote numbers from?

The illustrations explain processes and relationships; they are not a data source. Most deliberately carry few or no numbers, and any values they do show are simplified for clarity. The sourced figures, with their ranges and citations, live on the guide each illustration links to. If you need a number, such as a temperature range for Discus or a nitrite threshold, cite that guide or the printable aquarium charts, not the diagram.

When a fact file changes, the guides and charts update first. An illustration is redrawn if the change affects what it shows. If you believe a diagram is wrong or misleading, report it through the contact page, naming the illustration and your source.

Can you request a new illustration?

Yes. If you write about fishkeeping, teach, or run a club or shop and need a diagram that is not here, send a short description of what it should show and where it would be used via the contact page for AquaCompat. Requests that fit an existing or planned guide are the most likely to be drawn, because each illustration is made to support a page and its sources. New illustrations join this library under the same CC BY 4.0 terms. The verdict logic behind the compatibility diagrams is documented in the methodology.

Questions people ask

Do I need to link back, or is a text credit enough?
Online, link the word AquaCompat to the illustration's anchor on aquacompat.com/image-library/, as in the copied credit line. A link is the easiest way to meet the CC BY 4.0 attribution requirement, and it lets readers find the source guide. In print or video, where links cannot be clicked, a written credit with the full address is enough.
Which file format should I use?
Use the SVG download for print, slides or any layout where the image may be resized, because vector files stay sharp at any size and can be edited in Inkscape, Illustrator or Figma. The WebP image shown on the page suits web posts directly. Both carry the same licence and need the same credit line.
Can I use the illustrations in a paid course or a product?
Yes. CC BY 4.0 allows commercial use, including paid courses, books, apps and packaging, without a fee. The credit line must still appear where the illustration is used, or in a credits section that readers can find easily. You may not suggest that AquaCompat endorses the course or product.
Can I reuse the fish photos on the species pages under the same terms?
No. Species photographs are Wikimedia Commons images under their own licences, such as CC BY-SA, and each needs the credit and terms set by its photographer. Check the licence on the photo's Commons file page. Only the diagrams shown on this page fall under AquaCompat's CC BY 4.0 grant.