Small, large, from the reasonably priced to the prohibitively expensive, with and without extras. The description of pond filters sounds like comparing a Fiat 500 with a Porsche Turbo S. Unfortunately, we can rarely “test-drive” a pond filter to get an idea of its qualities, unlike with the €250,000 Porsche Turbo. This is actually a pity, because after just a few days it becomes clear whether the filter is any good or whether it should be written off as a "dead loss".
Let's first make a long list of what we expect from a pond filter:
- Clean, clear water
End of list
So there are our wishes in a nutshell. However, since many pond filters don’t even reach this target, it can’t be that simple after all. What is clear water anyway? Opinions differ here, as they do with "clean" and "pure". Some pond owners are overjoyed when they can vaguely recognise their fish, others want to see exactly what is lying around on the 1.80 m deep bottom.
A UV-C water clarifier (e.g. JBL PROCRISTAL UV-C Compact plus 11 W ) provides a quick and reliable remedy: its UV-C radiation in the range between 200 and 280 nm penetrates the cell wall of the algae and kills the algae. The flow rate of the water is important: if a too large pump is chosen, the UV radiation won’t be able to work to its full effect. Therefore please be guided by the recommended pump capacity! If the filter is connected BEHIND the UV-C water clarifier, the algae get caught in the filter and can be removed from the water system when the filter is cleaned. Without post-filtering, the dead algae re-enter the pond and sink to the bottom where they are broken down by bacteria. This again leads to an oxygen scarcity, as enormous amounts of oxygen are consumed by the bacteria during decomposition. In addition, nutrients bound in the algae (phosphates & nitrates) are released during decomposition and set the table for the next generation of algae. Therefore, nutrient limitation by a phosphate remover (e.g. JBL PhosEx Pond Filtre ) is 100% recommended after algae control. Unless you enjoy adding algae control to your weekly to-do list.
If your filter is newly equipped or just installed, please do NOT connect a UV-C water clarifier in front of the filter! The UV-C clarifier would prevent the filter from being colonised by useful bacteria that break down pollutants. After about 4 weeks of operation, each filter needs to be biologically functioning enough for a UV-C water clarifier to be connected in front of it.
Back to the actual filter: I could now list pages and pages of different filter systems from countless manufacturers. You often have the choice between stainless steel tanks and GRP (glass fibre reinforced plastic) tanks. Experts argue that the difference lies only in the price. GRP can be just as durable as stainless steel if the wall thickness is strong enough.
Two filter designs have become established: pre-filter and main filter with "biofilter material" and drum filter as pre-filter with or without downstream biofilter.
Since I prefer to sit by the pond and watch my fish rather than clean my filters, I prefer the drum filter version. The "dirty" pond water passes through a drum with a hole size of 40 - 70 µ and flows on into a container with biofilter material, on which pollutant-degrading bacteria settle that break down invisible substances such as nitrogen compounds (ammonium and nitrite). The water is thus cleaned mechanically (drum) and biologically (biofilter). The dirt causes the drum to become increasingly clogged, so that the water level rises. At a certain level, a rinsing of the drum is initiated, removing the pollutants from the water circuit. Perfect for lazy people like me!
The other variant with a pre-filter chamber also works splendidly - but only with hyperactive pond owners who are always looking for something to do.
The most important thing with ALL pond filters is getting the right size. After consultation with some pond experts, this is the main cause of cloudy ponds, because practically every pond filter works if it is the right size for the pond. Now, of course, everyone expects a clear statement: a 10,000 litre pond needs a xy litre capacity filter with a xy cm drum. And this is where it gets tricky: Besides the pond volume, many other factors play a role: How many fish live in the pond? How many plants and which plants have been put in (and not yet eaten up again)? Is there a marsh zone and if so, how big is it?
Back to the car comparison: a visit to your professional pond specialist shop is just as advisable as a visit to your local Porsche dealer if you want to express your wishes, analyse them and then implement them with the right equipment.
It is interesting to note, however, that worldwide the most Porsches are sold in the USA, a country with a maximum permitted speed of 120 km/h. So not everyone wants to drive 330 km/h in a relaxed manner, but the feeling of driving a beautiful car comes BEFORE the actual performance. And here we are again with an exclusive drum filter made of stainless steel...