Once a tank is filled and the fish are in, the substrate is the one part of the whole set-up that never gets touched again - which is exactly why the colour is worth choosing carefully the first time, not adjusting later.

This is Pettex's Roman gravel in Rosso Red, sold in a 2kg bag. It shares the same silicate aggregate base as the rest of the Roman gravel range, coated in a colourfast resin so the red does not fade or bleed into the water over time. Pettex say it will not change the water's pH, and the fine grain size makes it usable as a planting medium, with the increased surface area supporting anaerobic activity.

• 2kg bag of decorative aquarium gravel
• Colour: Rosso Red, coated in a colourfast resin
• Made from silicate aggregate, chosen for being chemically inert
• Pettex state it will not change the water's pH
• Suitable for coldwater, tropical and saltwater set-ups
• Fine grain size, usable as a planting medium

What the label does not say. As with the rest of this range, there is no stated grain size in millimetres and no per-litre coverage guide, so how many bags a given tank needs is down to your own judgement rather than a chart from Pettex.

Who it's for: anyone rescaping a tank who wants a strong red substrate rather than the more common black or natural tones, and who needs it to work across coldwater, tropical or marine set-ups.