Usually filtering doesn't work for biofilm and algae because the spores are so small they get through filters (even R.O.) and then grow downstream. The cheapest, most effective prevention is using chlorine but that's not good for the soil, especially for no-till, organic gardening when you want to cultivate beneficial microbes. Hydrogen peroxide is better – when you notice a problem, use 0.1 oz per gallon of water in reservoir. It dissipates much more quickly and because Blumats have such a low flow, there's a good chance it will be gone by the time the water gets to the plant roots. It's still a danger though for the good things in the soil. The best choice is probably Omri listed ZeroTol 2.0 made by BioSafe Systems