? PURE+ Filter Start Gel is a live, concentrated bacteria culture for use in new pond filters ? The gel based solution will stick to the filter media, allowing the nitrifying bacteria it contains to rapidly colonise your filter ? Once the filter media has been coated with the PURE+ Filter Start Gel, the beneficial bacteria within the gel will speed up the maturation of your filter media, while helping to convert ammonia and nitrite, resulting in less stressed fish ? Available in 2 sizes: 1 Litre treats ponds up to 10,000 litres, 2.5 Litre treats ponds up to 25,000 litres