*Delivery can be delayed by 2-3 days during busy times as filters are made to order*
Invisible / Hidden filter for normally stocked tanks up to 100 litres (26 US gallons) or as an additional filter to reduce nitrate. This video shows exactly how it is made and how it functions

This filter is made from the 'Hobby Coober Rock 2' resin rock which is 31cm x 14.5cm x 19 cm (12" x 5.75" x 7.7"), it comes ready to plug into any USB outlet and contains the following: 

1 x Coober Rock 2
200 lph (52 US gal.) USB water pump
800g of Biohome Plus
Coarse density foam
Medium density foam
Fine pad 
1 x 'S' hook (so filter can be used mounted to the side of the tank)

The 'S' hook can be bent to allow for thicker / thinner tanks to get a close fit between filter and glass.

If you want to make this filter yourself this video shows exactly how to: 'Invisible' Filter and the materials used for the DIY build are listed below:

The foams ('Foams' page) and filter media (Biohome' page) are available on the FilterPro site http://www.filterpro.co.uk
Hobby 'Coober rock 2': https://geni.us/uQRLcrB (The rock '1' and rock '3' in the Coober range are too small to make filters from but when used in place of natural rocks sitting on the substrate they compliment the invisible filters perfectly)
USB 200 lph / 52 US gph water pump: https://geni.us/SBPg1p
Dremel Milti-Tool: https://geni.us/LAdBKEB (There are plenty of Dremel Multi-Tool copies available at a cheaper price - I've got no experience of them as mine is genuine Dremel, still working well after many years)
Milling (cutting / drilling) bits for Dremel: https://geni.us/U0RS
'S' hook to hang the pump version: https://geni.us/oRsDTd (I couldn't find the exact hooks I used but these are the same dimensions)
The air stones and air line are available everywhere.