- Keep nitrates, phosphates and silicates at a low level. If you have a persistent problem - use reverse osmosis (RO) or deionised (DI) water, or specific adsorption resins (e.g. PhosGuard). However, note that although high levels of such nutrients may encourage algae, it is not generally possible to completely eliminate algae by attempting to reduce them, as algae can survive at levels below those which can be measured by a hobbyist test kit.