Part 7: Biological Filters – Bead, Tower and Vortex Filters

In part 6, we discussed the biofalls type filters, Big and Little Sister filters and Hydro Max filters. These are all filters using polyester pads as media.

The next type of filters to be considered is the bead filter. Bead filters are pressurized vessels. The bacteria grow on little plastic beads.

Bead filters consist of a sealed container with piping inside, a multi-part valve capable of reversing the flow and filter media. They work by pumping water through the slurry of water and beads. Because the beads are constantly in motion and getting fresh water, they are capable of supporting large amounts of bacteria. The constant movement of the beads allows for only the strong bacteria to stay on the beads and grow. Because the beads and bacteria trap dirt, slime builds up on the beads caking them together and causing channeling. To clean this out, all bead filters have a method to reverse the flow of water to flush out the debris that has built up. This process is called backwashing the filter. Some bead filters use a mechanical device to help break the beads up so that less water is used to backwash. Most bead filters use an air blower to accomplish this. While air is very effective at doing this, another device used for this purpose is a paddle that is hooked up to a motor to stir the beads during the backwash.

Following are some of the problems associated with bead filters. These filters do clog up and require backwashing. As they get clogged up, the flow slows down and less and less water is filtered. The flow becomes torpid and the bacteria that convert nitrite to nitrate can not grow. The bead filters are not designed to be an effective mechanical filter, therefore some type of mechanical filter needs to be used in conjunction with them.

Bead filters do have good points. They can handle large fish loads in a small foot print. Because they are pressurized, they can be located away from the pond. Due to the fact you must back wash them, you are forced to do routine water changes which is good for your pond and fish.

The next type of filter is the trickle tower filter. A trickle tower can be a very effective filter. It is a column filled with media such as bio-balls. Water is then trickled in at the top and flows down through the media, out the bottom and back to the pond. This allows the bacteria to take oxygen directly from the air rather than the limited amount of oxygen from the water. For the trickle tower to work correctly, a rotating spray bar delivers water over all the media to reduce channeling. Because the water is exposed to the air in very thin layers, the water will give up a great deal of the gases that have dissolved in it.

At this time, I have not seen any trickle tower manufactured for garden ponds. Therefore, most that are being used are homemade or made for the aquaculture industry.

A potential problem is getting the pond water to go over all of the media randomly. Because ponds tend to have a lot of dirt and algae, most spray bar setups are prone to clogging. Then there becomes the problem of making the filter large enough and with enough flow for the average pond without having the filter stick out like a sore thumb. However, a trickle tower can be very effective at biological filtration, but is a poor mechanical filter.

Vortex filters are mechanical filters designed to remove debris that has been sucked up by the bottom drain. They work by swirling water slowly in a chamber. The debris in the water settles out to the bottom of the chamber. The chamber has a drain on the side so the debris can be removed. It is the purpose of the vortex settling chamber to remove the debris that settles to the bottom of the pond so that the bacteria do not have to break it down.

If used correctly, the vortex filter can work very well. Unfortunately, most people aren’t using them correctly. They try to put too much water through and the debris doesn’t settle out properly. Because the flow rate is rather slow, the bottom drain that is hooked up to the chamber can not suck debris that is not right next to the drain. In this case, it is important that the bottom of the pond and the plumbing be designed correctly. In addition, the number of drains for the size of the pond needs to be correct. And the flow rate needs to be correct. Once set up correctly, they will work well.

Some people will try to use an air dome bottom drain with vortex filters. The idea behind this is that the column of air going up from the bottom drain will create a current of water that will help bring debris to the drain. There are two schools of thought on this matter. One is that the current starts above the drain and debris is sucked up in this current and never gets to the bottom drain to be removed. The other is that it works properly. The truth is that both are correct. The lighter debris gets caught up in the current and doesn’t end up in the bottom drain. The heavier debris does get moved closer to the drain where it is sucked up. So the decision to use that type of bottom drain depends upon what you want to remove from the water.

In part 8 I will discuss fluidbed filters, bioreactors, Nexus and other filter types.

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