Aquarium gravel isn't just decoration sitting at the bottom of a tank — it's also the surface most of a tank's beneficial bacteria actually live on, doing more for water quality than the filter alone gets credit for.

This is decorative gravel finished with an epoxy resin coating, which keeps it inert in water so it doesn't alter the tank's chemistry, while still giving bacteria something to colonise. It comes in a multicoloured 'Rainbow' mix, in a 2kg bag, suitable for both freshwater and saltwater aquariums.

• Epoxy resin coated, inert in water
• Doesn't alter tank water chemistry
• Provides a surface for beneficial bacteria
• Rainbow (multicoloured) finish
• 2kg bag
• Suitable for freshwater and saltwater aquariums

A naming oddity, for the curious. This 'Rainbow' colourway is sold under a different name — 'Arcoiris' — on Marina's own Spanish storefront; the manufacturer code and barcode are identical, so it's the same product rather than a different mix, just labelled differently market to market.

Who it's for: owners wanting a multicoloured decorative substrate that also does a real job for water quality, rather than plain gravel with no functional coating.