Coloured gravel divides opinion more than almost any other aquarium product — some owners want a tank that looks like a natural riverbed, others want something brighter, and either way the material underneath the colour matters more than the shade on top.

Pettex's Roman Gravel Spectrum Mix is chosen from selected silicate aggregates, in a mix of natural stones and stones coated in a colourfast resin, sold in a 2kg bag. It suits any type of aquarium set-up, including coldwater, tropical and saltwater, and Pettex state it will not change the pH of the water. Its finer grade also makes it a workable planting medium, with increased surface area said to support anaerobic activity in the substrate.

• Selected silicate aggregates, natural stone and colourfast resin-coated pieces
• 2kg or 8kg bag
• Suitable for coldwater, tropical and saltwater set-ups
• Will not change the pH of the water
• Fine grade, workable as a planting medium

On the colourfast coating. Some pieces in the mix are coated rather than left as bare stone, and Pettex do not give a lifespan for how long that coating is expected to hold its colour under normal aquarium conditions and cleaning.

Who it's for: owners who want a brighter, mixed-colour substrate rather than plain natural stone, without giving up on an inert gravel that will not shift the tank's water chemistry.