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.