Things to consider before you get a pond filter

.. you must get yourself a water test kit (for ammonia, ntrites, nitrates and pH measurement and possibly oxygen) and get proficient at using it and if you are colour blind, employ someone who isn't. Then by using this and processes of deduction (if it isn't already blatantly obvious) you can make your own conclusions about the need for a filter and subsequently, how effectively it is working.

ALSO consider the type or style of your pond. There are different solutions to different problems in different pond environments. For instance it would be silly to try to use a filter on a conservation/natural style of pool where the very definition of that type of pond dictates the encouragement of the ecological and self-contained cycle within the pond. Besides which, many of these pools have soil bottoms, apart from containing all the necessary bacteria, this would soon clog up the pump and filter system. These ponds need plants to keep them clear.

By the same token, it would be ludicrous to try to diminish the maulm or detritus in the bottom of the pond using a filter whilst at the same time using one of the clayey type bacterial activators for the bottom of a pond.

Some people like to cure problems with a sledge-hammer type of approach, buying the most lethal algicide obtainable, dosing their pool with the maximum and then bemoaning the return of the problem in less than a fortnight, or crying with self pity when all the fish have died.

The number of chemical cures for pond problems is mind boggling.

[An algaecide manufacturer once told me that the product he sold on the retail market was nearly half the strength necessary to provide the correct dosage at the dilution rates described on the bottle. He said that when they used to supply the stuff at the correct concentration, which for the correct quantity of pool water would be positively effective, they were always getting complaints of dead plants and even deader fish. So now they dilute it, the customers are happily 'overdosing' and all they get is letters of approbation.]

To other people, the chemical approach may seem abhorrent, but it may be argued that their problems could be cured by, perhaps, a single dose of algicide just to get the seesaw effect of the natural pond environment more consistently on the permanently clear side. However, Barley straw, a natural 'Pond Start' chemical, a bag of Daphnia or even a dose of the water from a successfully clear pond may be enough to get the pond to a permanently clear state.

Another problem maybe the pH or hardness of the water: a high pH encourages some forms of algae, in particular the thread type algae often referred to as blanket weed. It is possible to adjust the pH with chemicals or a plastic 'teabag' of peat pellets floating in the water. Stop fresh cement leeching lime into the pond by sealing it or treating it with silglaze.

Blanket weed or thread algae can be related to phosphates and hard water (high pH), and once you have it, it is very difficult to completely eradicate. One advantage is that you very rarely have problems with other algae once it is established.

Also stop topping up with high pH tap water.

If you have a filter and it does not seem to be working it be because it is new and new filters are slow to mature. Besides if the algae problem is caused by those types that cling together, like the globular jelly types, or grow in strands like the blanket weeds, a filter by itself is not going to solve the problem. Green water with a biological filter in the equation is a whole new topic.

So here is a reminder of the parameters for effective filtration, before we consider what else can be wrong.