Biological Filter Maintenance

I flush my biological filter system regularly (weekly) as part of the partial water changing routine but in terms of a real good cleaning, it would be once a year or even longer sometimes. What triggers me to do it?

Well, I usually do this when I noticed that the water level in the return pump chamber falls below the usual level. My filter system consist of several chambers and uses gravity to move the water from the first chamber (with the inlet from the pond) to the last chamber where the return pumps pushes the water back to the pond. A fall in the water level in the return pump chamber signifies that there is some “resistance” to the water flow within the filter system. This is normally caused by clogging of the biological filter mats and/or the cockles shells and crushed coral chips I used for PH buffering and biological filtration. Hence a more thorough back-flushing or good cleaning of the biological filter is needed.

Cleaning Steps

1. Stop the return pumps. 

2. Insert the standpipes to stop the pond water from going into the filter. Note: as I am using venturi pipes, the water could backflow into the filter through them until the pond water level reaches the level of the venturi pipe. In any case, the venturi pipes are about 4 to 6 inches below the normal pond water level.

  Picture showing the Standpipes in the filter chamber. Some are not inserted yet. Sockets for the standpipes can be seen at the bottom and water comes into the filter from the pond’s bottom drains through them.

3. Open the specific ball valve in the sludge chamber for the selected filter chamber.  Water will reverse flow down the chamber through the bottom drain in the selected filter chamber and goes into the Sludge chamber. This is known as back-flushing the filter.

  Picture showing the ball valves in the Sludge chamber. Drain pump comes with automatic cut-off system that stops the pump once the chamber is empty of water.

4. Turn on the Drain Pump in the Sludge chamber to empty the Sludge chamber. 

4.  If I am cleaning the filter mats, I would not remove them from the chamber since they are placed vertically and I could clean them with a hose. I would just hose them down with water and drain the dirty water out through the bottom drain in the filter. Theoretically, tap water should not be used since tap water contains chlorine and chlorine kill bacteria in the filter mats. Best is to use pond water but I have been using tap water without any major consequences. The trick is not to over-clean the filter mats until they look brand new again! You still need the denitrifying bacteria for biological filtration. Instead, just give them a good flush and leave some brownish “dirt” behind. These “dirt” are the bacteria and they will soon multiply and colonise new bacteria when the filter system is put back into operation.

5. If I am cleaning my crushed coral chips and cockles shells, I will remove about half of them from the filter chamber so that I am able to clean the media at the bottom of the chamber. Placing them in sacks, made from nylon nettings, help facilitates removal from the chamber.  The removed sacks are hosed down with tap water.  I will hose them down the remaining sacks in the filter chamber (with tap water, of course!) and then drain the water out through the bottom drain.

6. I do not clean all the chambers at one go. Cleaning may affect the effectiveness of the biological filtration until the bacteria has time to grow and settle. I usually flush 2 out of 3 of my biological filter chambers, leaving one chamber for the next time. This will avoid a potential for a nitrite and ammonia spike in the pond due to lower level of biological filtration after the filter cleaning.

7. After cleaning, I remove the standpipes, one at a time. I will see a big gush of water from the pond into the empty filter. This is good as it flushes the pond’s bottom drain pipes leading into the filter system and removes the muck that has settled at the bottom drain pipes. Have to reinsert in the standpipes before the water in the first chamber overflow into the second chamber.  Do not want this muck to go into the cleaned filter. Now is the time to flush out the first chamber (standpipe chamber or settlement chamber). I repeat step 7 until clean water is coming into the filter from the pond, i.e. pond’s bottom drains are cleared.

8. Close all ball valves in the sledge chamber and turn off the drain pump. My drain pump has an auto cut-off that stops the pump once the sludge chamber is empty.

9. Refill the pond. Add dechlorinator to your tap water if you are refilling a high percentage of pond water using tap water.

10. Turn on the return pumps once the water level is high enough for the filter to operate.

The whole cleaning process takes about an hour and is a good workout. Cleaning the filter media could be quite messy, especially if you have to remove them from the chambers. Wear protective rubber gloves if you cannot handle muck.

Plants for Koi pond - Lotus

The lotus plant can be grown in pots placed in the shallow part of a Koi pond. Protect the top of the pots with large stones to prevent the large Koi from digging on the soil and messing up the water. The plant has two types of leaves. Some that grows above the water surface (as shown in picture below) and some that floats on the water surface. The plant produces pink flowers on a long stock above the water .

 

The above picture was taken in Ocean Park, Hong Kong on a recent trip there.

Besides the Koi pond, the park has an interesting section showing many varieties of Chinese goldfishes and describes how the modern colourful goldfish varieties originated as a natural mutation of the Crucian Carp (Carassius Carassius), which was originally a drab olive colour.  A natural mutation resulted in some orange-red colour goldfish. This led to selective breeding for over 1000 years to produce the various varieties of modern goldfishes.

Plants for Koi Pond – Elephant Ears (Alocasia Macrorrhiza)

  

The Elephant Ears or Taro (Alocasia Macrorrhiza) is another common plant found in South East Asia. This is a relative large plant with large leaves that grows well in a large pot placed in the shallow part of a Koi pond, with the pot half or almost fully submerged.  It propagates through small suckers that grows at the side of the large plant. The picture above shows a relatively young plant. A mature plant can grow to a height of 5 feet or more and have leaves that is more than a few feet in length. It will make a nice specimen or feature plant in the garden or in your Koi pond.

I surround the Elephant Ears with the Creeping Daisy (Wedelia Trilobata) to hid the large pot and soften the overall look. The Creeping Daisy has small yellow flowers and is easily grown by stem cuttings. Just cut and stick them into the wet soil in the pot.  It roots easily and further cuttings can then be made and inserted into the pot again. In no time, you have a nice covering of Creeping Daisy with yellow flowers around the large leaves of the Elephant Ears.

  Close up of the Creeping Daisy

As the pot sit in my pond, I do not add any fertilisers to the soil. I guess the plants will just absorb the  nutrients and nitrates from the pond water.

Water Quality Testing in Koi or Fish Pond

Water quality testing is important, especially when you are starting a new fish pond or filter. This is the time when the bacteria in the biological filter is trying to grow and establish itself and ammonia, nitrite will be present in the initial stage of nitrogen cycle. During this time, risk of fish fatality is high and pond keepers will not risk putting in expensive, show grade Koi until there is no ammonia or nitrite present, as determined by the water quality testing. Instead, most pond keepers will put in small feeder fish or low grade Koi to produce the needed fish waste to feed and cultivate the bacteria in the filter. It normally takes a few weeks for the biological filter to establish itself. 

Other times when water testing should be done is when you have recently added more fish to your pond. This is the time when the water parameters will deviate from the norm as the filter adjust to the new load of waste matters coming from the increased population.

I am using the Tetrapond Laborett test kit. It tests pH, carbonate and general hardness, nitrite, ammonia and carbon dioxide. I also use the individual test kits for oxygen level and nitrate.

pH is a measure of the acidic or basic (alkaline) nature of a solution. Normal tap water or fresh water should have pH level of 7. Water with a lower pH level is deemed acidic while alkaline water would have higher pH. Chalk, limestone, coral or seashells dissolved in water will produce higher pH. pH level is usually determined by your water supply. Koi requires a pH slightly above 7. The best way to control pH is to include crushed coral ships or seashells as one of your filter media. The carbonate in them will acts as a buffer against sudden, sharp drop in pH level which kills fish swiftly.

Oxygen level testing is important to determine if you have enough aeration in your pond to support the fish and plant population in your pond. I do this at the onset of a new pond or when I add more fish to my pond. Once you have the right level of aeration, the oxygen level seldom fluctuates a lot unless you have a broken pump. I actually notice small bubbles forming at the sides of my pond when sunlight is shining on the algae that grows on the side. I think this is a good sign of oxygen level saturation and my aeration level is sufficient.

Nitrate is an output of your biological filter. Nitrate is harmless to fish in small quantities but as mentioned in my earlier post on the need for regular partial water change, nitrate level should be kept low. When the nitrate level goes beyond the level indicated in the test kit, it means it is time for partial water change. I actually stop doing my nitrate level testing and just do my regular partial water change as a routine. Other symptoms of excessive nitrates will be excessive algae growth (greenish water) or brownish tint in the water.

In the beginning of my Koi hobby, I used to test regularly and log down the readings in my excel spreadsheet. As I get more experience in pond and koi keeping, I actually stop performing water quality testing although I still have my water testing kit on standby. Maybe this is not a good trait of a good koi keeper but then, that’s me. I stick to my regular partial water change routine, regular filter maintenance and I know that my pond and filter is well designed to produce good water quality. I observe my Koi’s behaviour daily during feeding. My water test kits will be used immediately when I notice my Koi behaviour changes. So far, so good!