Pond Skimmers ... also called Surface Skimmers

I don't think I have ever discussed pond skimmers. A pond skimmer is designed to remove (skim) floating debris by suction and thus remove some of the potential biological debris polluting the water or making it cloudy.

The skimming action is created using a pump which can be attached to what is a fixed or floating device ... for those people with swimming pools the skimmer is almost always in a fixed position and is normally an overflow point. Inside a pond skimmer is normally a plastic mesh or wire basket which catches the debris sucked into the pond skimmer unit. The size of the mesh determines what size of solid can pass through the pond skimmer ... this means a solids handling pump matching the mesh size must be chosen. Fixed pond skimmers sit on the bottom of the pond or on a brick to elevate them depending upon depth.

This type of pond skimmer will normally have a base which can somehow be weighted with stones to prevent it moving. There will be a device for connecting a pipe leading to the pump at the base of such a pond skimmer. Some pumps have a separate nozzle to attach a pond skimmer to. Pond skimmers are normally not an essential part of an average garden pond.

Not An Ordinary Pond

This story was submitted by Vin Quesnel from Trinidad close to Venezuela.

I am a new-comer to ponds.

 I have a large pond or maybe a small lake.It covers about half an acre and has a small island.I built it about a year ago where I live on the edge of the jungle.Its fed by a ravine which dries up in the dry season. Its 8 to 10 feet deep.

Its different from the ponds I am now beginning to read about in your publications which I was led to in my search for a means to clear up the water.I have no koi, just native fish like whabeens, river sardines, scavengers (tetas) and some tilapia. Weve caught a 12 inch whabeen but most of the fish dont get beyond six inches. Our problem there is the alligators (caimans) eat them before they can get big! The last alligator we killed was five feet but weve seen bigger though not recently as all the edges are better kept now.

First the lake was overtaken by hyacinth lilies which we were able to get rid of.Now we have plenty cabbage lilies but they have not flowered yet. The surface is over-run with duck weed.Were taking that out now and putting in some ducks which I am told will eat the duck weed.We have to wait for the ducks to get quite big before we release them otherwise they get attacked by the hawks.I have seen a big black hawk fly off with one of my full grown chickens in its claws!

I live in Trinidad, an island just off Venezuela, so we get Venezuelan wild life washing ashore on clumps of land when the Orinoco floods. My project now is to get the water clean which is why Ive "joined your club".

I face such different problems.While most of you worry about the color of your koi and the lighting of your pond Im fighting alligators and hawks!!

Thanks a lot Vin ..... somehow I don't think my book will help a lot!!!

2. Pressurized Pond Biofilters

Last week we did the annual exhibition of our fibreglass water features at the UK's premier garden trade show called GLEE. The show is massive and held every year at the National Exhibition Centre in Birmingham.

I have been going to this show for 11 years and always try to "discover" what's "Top Of The Pops" ..... by this I mean not what is new and revolutionary but what has been adopted by the industry in general and has become something of a standard offering. This is a sure sign of success in the marketplace.

This year the product that everyone was offering was the pressurized biofilter and UV combined. The first company to offer this type of filter was Hozelock Cyprio around 5 years ago.

Most pressurized biofilters are basically cylindrical in shape with inlet and outlet pipes close to the tight fitting lid.

As such a pressure filter is essentially a container that can be operated under pressure and inside which is a mechanical filter system and an UV lamp. The mechanical filter system is normally open celled foam which doubles as a filtration biomedia.

The better models also include additional biomedia like Alfagrog.

The single biggest advantage of a pressurized biofilter is that it can be buried and placed anywhere in the pump circuit (even below the pond level) making hiding much easier than with a box type biofilter.

The first thing you will notice about any pressure biofilter is that it is very compact and immediately begs the question why can a pressure filter be so small yet do the same job as a CONSIDERABLY larger conventional biofilter. Those readers who have been with us for some time will probably know the answer. For the newcomers let me explain ....

The effectiveness of any biofilter has nothing to do with the size of the container. It has much to do with the type of biomedia used and also the effective turbulence produced around the biomedia in the filter itself. You should read my coffee and sugar example to better understand this idea. The higher the turbulence the better is the dissolved oxygen and nitrogen food component placed in the immediate vicinity of the filter bacteria. In this way biofiltration efficiency is increased by an enormous amount.

This means the size of a container can be reduced.

A most important reason allowing the success of the pressure biofilter is the inclusion of an UV lamp which kills water-borne suspended algae. This flocculated algae is then removed in the mechanical filtration section of the pressurized biofilter. If there was no UV lamp then the sponges making up the mechanical filter would block very quickly and create excessive cleaning situations. Bear in mind that most cloudy ponds result from suspended algae and not dirt.

A pressurized biofilter cannot work effectively using a normal pond pump which contains a suction strainer sponge. It is preferable to run a solids handling pump directly through the pressure filter. When flow coming out of the filter falls off it is time to clean the sponges.

In the best models this can be easily and quickly achieved without opening the filter itself .... avoid any unit which requires opening to clean it. The pressure required to drive water through this type of biofilter is higher than required for a normal box type biofilter and this must be taken into account when selecting a suitable pump.

Special situations requiring extra attention

The capacity of a pressure biofilter when related to any pond is also a function of the fish mass inside the pond and not just the volume. The reason is that more fish produce more waste which means the filter will block up faster. In addition the larger the amount of fish mass then the larger must the pump be to keep the efficiency of bacterial nitrification at a high level. Remember as flow drops then operating efficiency also drops. This is an excellent reason for choosing a pressure filter with Alfagrog inside it. This allows high conversion efficiency to be maintained as the flow drops due to sponges blocking.

What this means in practice is that you must be very careful in selecting the right pressure biofilter and pump. If a unit is described as handling a pond of say 1,000 gallons this would only be the case if there were no fish (ie plants only) in the pond. If the same pond had goldfish then the capacity might drop to say 500 gallons and with koi it could drop to 250 gallons ..... see what I mean?

In summary

1. Choose a pressure biofilter with extra biomedia inside it (not just foam)

2. Choose the size bearing in mind the stated capacity is normally for pond with plants only so read the instructions carefully

3. Choose a suitable (higher pressure, no sponge) pump

4. Choose a pressure biofilter with easy cleaning mechanism.

3. Feeding Fish

During mid summer a fish can easily eat 1% of its body mass. This will reduce as water temperature falls. So the amount of food you can feed your fish can feed depends upon water temperature.

Here is an approximate feeding guide per single fish based upon very average situations at 20 degrees C (68 degrees F) so do not take these figures as absolutely correct under all circumstances. Rather use it as a guide.

6 inch fish ...... weigh about 2 ozs or 50 gms so feed 1% of this weight per fish per day in total 12 inch koi weigh about 400 gms or 14 ozs so feed 1% of this per fish per day in total

You can leave fish for a week and more quite easily without any feeding

At about 15 degrees C (59 degrees F) reduce food by 1/3rd and at 10 degrees C (50 degrees F) reduce to 1/10th

1. Do NOT overfeed fish.

2. Do feed small amounts more often than a single large amount

3. Remove uneaten food before it sinks.

4. If you have mixture of large and small fish grind the food up into smaller particles to give the smaller fish a chance to eat before the bigger ones gobble up the larger particles.

The reason for all of the above 3 tips is that the amount of food fed has an almost immediate and direct impact upon water quality and biofilter load.

Water Gardens Gazette number 320