WIO > Boulders

Boulders are the largest format WIO makes — 21 kg boxes of rounded, weathered stone for tanks big enough to carry it. This is centerpiece material, and it solves a problem that smaller rock cannot: giving a large tank a single object with enough mass to hold the composition together.

When a boulder is the right answer

Large tanks defeat small rock. Spread a box of fist-sized stones across a six-foot tank and you get texture without structure — nothing for the eye to settle on, and a layout that reads as scattered rather than composed. One properly scaled boulder, placed off-center, fixes that immediately.

The rounded, water-worn form also says something specific: this is a river bottom or a lake margin, not a mountain. Angular stacked stone reads as exposed bedrock; boulders read as stone that water has been working on for a long time. Pick the one that matches the biotope you have in mind, and do not mix the two in a single scape.

The three families

• Black Venom — near-black, dense, heavily textured. Maximum contrast against planting, and it makes fish color look saturated. Algae shows on dark stone, so it suits a tank you keep on top of.
• Bumblebee — banded light and dark. Strong character; one is a statement, two start competing.
• Zombie — mottled and weathered, the most naturalistic of the three and the easiest to make look like it was always there.

Each has matching sands and riverbeds in the same family, which is the point of buying into the system.

Weight, and the thing people forget

21 kg is roughly 46 pounds, and that is before you add water, substrate and the rest of the hardscape. Two considerations:

The stand. A large planted tank with heavy hardscape is a serious floor load. Check what the stand is rated for and, in an older building, think about where the tank sits relative to the joists.

The glass. Never set a boulder directly onto bare bottom glass, and never let one rest against a pane. Bed it on a layer of substrate, or better, on a piece of eggcrate or foam underlay that spreads the point load. Stones placed hard against the glass during a rescape are a common cause of cracked tanks, and it usually happens weeks later, not at the moment of placement.

Placing one

Decide the boulder's position before anything else goes in the tank; everything else is built around it. Off-center, roughly at a third of the tank's width. Tilt it — a boulder sitting dead level looks placed. Bury a third of it, which both anchors it and makes it read as far larger than it is.

Then get help lifting it into a tank with water in it. Wet hands, 46 pounds and a glass rim is a bad combination.

Chemistry, at this volume especially

WIO publishes no hardness or pH data. At 21 kg of rock the surface area in contact with your water is substantial, so if you keep soft-water species it is worth the ten-second check: white vinegar on a dry surface, fizzing means carbonate content that will raise KH continuously. For community fish and Neocaridina on San Diego's hard tap water this is not a concern. See aquascaping stones for the full explanation.

Come and choose it

Nobody should buy a centerpiece stone from a photograph. Shape decides everything, and a boulder is the one piece in a scape you cannot work around if you dislike it. The Convoy store keeps WIO on the floor — come and look at what is in stock, and we will help you work out whether the scale is right for your tank before you carry it out.

Smaller tank? See WIO nano stones and boulders.