30 fishtank filters (West Croydon CR0)

These are used to lock together to fit in your big tank, thrn you add the air bubble & pipes not included here, but can buy very cheaply on amazon. Then once placed on bottom of the tank you put your gravel or stone over this to cover, & it helps to keep tank clean as the bubbles keep it filtered for a long time 6-12 months. I have changed my system recently so no longer need these. Collection ASAP or I might put in for recycling. Thankyou.