Hints and tips for gardening and pond life

1. Do not use tap water in cleaning the medium or any of the filter elements. The chlorine in the tap water will destroy the valuable bacteria.

2. If you have to top up the pool with tap water, let the water spray in from a height. This dissipates the chlorine. Add a pool conditioning chemical to help the fish cope.

3. Dont use the u/v below 10C. It will kill off all the algae in the pool, which is not necessarily a good thing.

4. If there is an algae bloom in early spring, dont worry. It may be a sign that the system is working to the extent that ammonia and nitrites are being broken down to nitrates and this is what is causing the algae to proliferate. Everything will eventually even itself out.

5. After long periods of very cold weather, particularly if you have allowed the medium in the filter to freeze, it is best to start again with fresh medium, unless of course it is one of the modern plastic open types.

Spring cleaning the biological filterStep-by-step

Spring is here and the water temperature has soon risen to a level at which it encourages plenty of biological activity. The filter is at the top of the stream on this pool, which has a header pool full oxygenators to help with the water treatment. The filter is only just large enough for the pool size, so a regular 6 monthly thorough service is undertaken just to ensure it will cope for the following season.

The pool is still clear, so things have not got desperate yet. The state of the biological filter will confirm this.

2. The biological filter box is situated at the top of the waterfall in a chamber to disguise it. The water supply to the filter is a measured * amount that comes from the main supply to the top header pool of the stream from the submersible pump in the pond below. (*Simply calculated by timing the filling of a 2 gallon (10litre) bucket of water from the filter supply pipe, or measuring the volume that comes through in a minute and multiplying up the result by 60 to find out the volume of water coming through in an hour. This should correspond to the volume of water the manufacturers of the filter claim can be processed by that filter. This in turn should work out at roughly half the volume of the pond coming through the filter every hour.)

This filter has a U/V Clarifier to help it; that is what is sitting on the top.

3. First of all the U/V Clarifier is disconnected. The old plastic pipe moulds itself to the hose-tails and needs a little gentle persuasion with a screwdriver to release them. A smear of waterproof grease from the last service makes this a little easier as does grease around the jubilee clips.

The gate valve that controls the flow from the main supply to the stream can be seen below. If I turn this off, the stream can continue to run unabated whilst I dither around.

The U/V is removed to the side and the lid of the filter box is taken off. The filter foam looks relatively clean, which is a good sign that the biological action of the filter is working efficiently already this early in the season.

4. The foam is removed to reveal the bulk of the main filter medium. In this filter we have the expanded clay granules that are used in hydroponics (it is sold under brand names like Hortag or Leica).

5. The brushes that hang in the settlement chambers are also removed. This is the chamber where the dirty pool water first enters the filter after coming through the U/V. It is sprayed over a plastic grid and falls down through these plastic flue brushes. In the process the large pieces of muck and detritus in the water are held back by the brushes and tend to collect there and in the bottom of the chamber.

This filter is my preferred filter design because it is easy to back-flush a lot of this bulky muck out on a regular monthly basis by just removing the drain plug at the base of the unit. Also the water rises up through the main filter medium fairly evenly and relatively slowly compared to gravity fed filters. There is also the added advantage that filters like these that return water to the pool from the top of the unit are that much easier to disguise. This one for instance could be buried up to its lid to hide it from view.

7. Looking down into the settlement chambers (where the brushes were) we can see the water looks black and slimy. An investigative feel reveals a build up of glutinous sediment the bulk of which ought to come out. The drain plug for the unit can just be seen on the outside at the bottom.

Unscrewing the drain plug releases the water in the filter box, dragging out with it a lot of the sediment. This saves bailing out a lot of the sludge, which empties out into the stone chamber and in turn drains into the rockery beds.

9.  Whilst the filter box drains, I scoop out the filter medium with an old aquatic planting basket into a bucket with a crack in it. An overhead view of the filter box draining out into the chamber. Having scooped out a lot of the filtration medium, we are now reaching the level of the perforated base.

10.  This perforated base, that is the divide between the settlement chamber and the filter medium, is lifted to reveal the sludge. This can soon build up to a level where the settlement chamber is blocked to the flow of water.

11. The sludge that could easily build up and block the filter is removed.

12.  Over at the water butt, I clean the filth off the perforated divider. This needs to be as clean as possible to allow easy movement of water through the filter. This could be done in a bucket of pond water but not under the tap. We want to encourage the rapid reinstatement of the bacteria in the filter. Any traces of chlorine in tap water will hinder this.

13.  The filter brushes are given a good rinsing through.

14. The cracked bucket is handy when rising through the filter medium. The pores in the expanded clay contain the valuable bacteria that break down the organic matter, including the dead algae, that comes through the filter. This definitely needs to be kept well away from tap water. It is usually unnecessary to replace it. If for some reason you wish to, retain some of it as a starter for your new batch.

The sponge is rinsed through as well. If this is the correct material, the open pores should run right through the thickness of the material, making it easy to clean and allowing even passage of water through it. This too will be full of valuable microbes so dont be too diligent in the douching.

15. The submersible pump in the pond is turned on at the junction box so the supply of water to the filter box from the inlet pipe can be used to wash out the filter box itself. I can use it to hose down the inside of the filter box. It does not have to be super-clean or spotless.

16. The perforated base/divider is replaced (the right way round).

17. The sediment brushes are replaced. It is often easier to put them all in together whilst already hooked into the perforated plastic strainer from which they hang. Dont forget the drain plug either with its important o ring seal.

18. Pour back the filter medium. You may find that some has gone the way of all flesh and a top-up is necessary to achieve the original level. Not too much though...

19. ... When the sponge goes in it must be well below the outlet back into the pond. Reconnect all the hoses with a smear of grease on the hose tails and the clips.

20.  Before the system is turned on again, remove the submersible pump from the pool, take off the prefilter/strainer and check that the impeller is clear of detritus. This is the real mechanics of the whole system and needs very regular checking to ensure efficiency.

21. If there is no U/V Clarifier to service then turn the system on. Watch the filter fill to running to ensure the foam filtration pad does not float up to block the outlet. Also check that the inlet over the sediment filter brushes is not so vigorous that it is spraying all over the place.

Put the lid on to the filter and check all the hose tails and joints and around the rim of the lid for any drips. Take appropriate action if there is.

22. Sometimes hose-tails, if they are disturbed, need to be replaced with a few windings of plumbers PTFE tape wrapped around the threads. Start from the bottom of the thread and wind up to the top, following the line of the thread.

24. Finally check the outlet into the top of the stream for any drips back or magically sideways, backwards or upwards hairline rivulets of water.

If the stream seems to be flowing better than it has done for a long time, check the stream itself for any areas where it may be backing up to overflowing with the more fervent water supply.