The aquarium shirt that's actually about water

A cross section through a planted tank: substrate layered at the bottom, roots reaching down into it, a filter intake at one side, three fish holding at three different depths. In the corner, a small table — pH 7.4, KH 6, 24C.

Nothing about the fish is the point. Everything drawn beneath them is.

Why cut the tank open rather than draw it from the front?

Because the part a keeper actually manages is the part a front view hides.

Substrate composition, root depth, flow off the filter, where the warm and cool layers settle — none of that is visible looking at a tank through the glass. A cutaway shows the mechanism the hobby runs on instead of the display it produces. It's a different relationship with fish entirely from the one anglers have with the ones they're trying to catch — keeping something alive rather than landing it. The fish here, drawn small and mid-water, are the one decorative element in an otherwise technical drawing.

What do the three numbers in the corner mean?

A complete description of the water, to somebody who reads it fluently.

pH 7.4 is acidity. KH 6 is carbonate hardness — a buffer that stops the pH swinging when something goes wrong elsewhere in the tank. 24C is temperature. A keeper who's cycled a tank can reconstruct roughly what lives in that water from those three figures, the way a mechanic reads a spec sheet. To everyone else it's three quiet numbers in a corner, and that gap is most of the design's appeal.

What makes a good aquarium cutaway, specifically?

Legible layers, in order: substrate, roots, flow, fish.

The substrate wants a visible grain or gradient so it doesn't collapse into a flat band under the tank floor. Root systems should thin out rather than stop cleanly — real roots taper. The filter intake is one small, precise shape rather than a mechanical diagram; it only has to register as "the water moves from here." Fewer colours hold technical line work like this together on fabric far better than trying to shade it — two inks reading as depth, rather than six trying to be realistic.

Why black rather than a lighter shirt?

Because it's the ground line work like this is meant to glow against.

Cyan and coral on black behaves the way the tank would look through its own glass at night, lit from inside — a high-contrast graphic that holds its shape rather than fading into a wash of similar tones. On a pale shirt the same lines read as a diagram on paper: correct information, wrong feeling. Black is also the one background that doesn't compete with a parameter table sitting quietly in a corner.

Can it use a real fish species or a shop's tank-building style?

Species names are plain vocabulary; a specific retailer's or forum's house style isn't.

Common names for fish, plants and hardscape materials belong to nobody in particular. What does belong to somebody is a supplier's branded substrate name, a shop's signature aquascape look, or a competition's judging categories, if a design starts copying those rather than describing a tank in general terms.

Does this work for a reef tank instead of planted freshwater?

Yes — the cutaway logic holds; only the layers change.

A reef tank swaps substrate and root zones for live rock and a sump running underneath, and the parameter table swaps pH and KH for salinity and calcium. The drawing is still a cross section of what the keeper is actually maintaining; which parameters go in the corner is the one decision that changes between the two.

Does it print well?

Yes, and black is doing most of the work.

Line work this fine needs consistent stroke weight on black — thin lines that vary will fill in at the edges, so substrate grain and root hairs want to run coarser than the reference drawing would naturally render them. Cyan and coral read clearly against black without a third colour, and the parameter table's small type is the one place worth keeping crisp rather than stylised.

How do I get one made?

Describe the tank at JustOG — the layers, the parameters, and what's swimming through it. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.

Designs other people have published are in the shop.

pH 7.4. KH 6. 24C. Everything a stranger needs to know about somebody else's tank.