Selecting a drum filter is more difficult than it might seem. Most manufacturers only mention the maximum flow rate the drum filter is suited for. Oddly enough, most manufacturers don’t mention at what level of contamination (mg suspended solids) this maximum flow rate applies to…
A drum filter designed for a lightly populated pond with a maximum water flow of 25m³/hr will definitely not be able to handle 25m³/hr in a heavily populated pond. That’s why good filters mention the amount of pollution at which the maximum flow rate is achievable. The amount of pollution is given in milligrams of solid parts per litre of water. Ponds often use a value of 10 mg/l and fish farms 25 mg/l. However, fish farms use shorter flush intervals, the time between two flushes. It’s not unusual for a drum filter to flush every 2~3 minutes, continuously flushing drum filters are even often seen in fish farms. A flush interval between 5 and 60 minutes is more common for ponds.
A drum filter should not function on its maximum flow rate, at least that’s the advice. For an example, let’s say we’ve got a flow rate of 25m³/hr. If we can pick between two filters for this, one for 25m³/hr and one for 50m³/hr, the 50m³/hr one would be the best choice. This filter would have to flush way less than its little brother (less than 50%!) and the filter will also filter finer*. The water and energy consumption are also way lower, the panels will take longer to get fat and the filter needs less maintenance.
Too big of a drum filter also can’t be recommended, this will filter too fine despite the panels with relatively big mesh size. We advise to pick a filter that’s used to function on about 50% to 75% of its capacity.
Drum filter can be equipped with filter panels with various mesh sizes. We recommend a mesh size between 70 and 100 micron. If you’d filter any finer, the amount of flushes will increase and the biological filter won’t work as well! A biological filter needs organic pollution to function well. There won’t be enough organic pollution of the water’s being filtered too fine and its performance will then decrease.
*Just because a drum filter has filter panels with a mesh size of 100 microns for example, doesn’t mean it can filter (way) finer. This effect depends on the flush interval, the longer the flush interval, the finer the filter will filter. This is because the bigger particles will block the holes in the 100 micron mesh and smaller particles will then also be filtered out.