8.7.8. Small DIY Filters

People with small tanks need inexpensive ways to filter these aquariums. While I heartily recommend under-gravel filters for these small aquariums, many hobbyists do not want to go that way. They want a planted aquarium, soiled aquarium, or they want a sand substrate. Sponge filters are not liked by many because they are ugly. So below we describe some sixteen different alternatives.

First off we need to identify two different types of pumps to use in some of these designs:

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Equipment

There are two types of pumps I will use here-in. One is a powerhead pump, and one is a small 12 volt fountain pump.

All these designs use only K1 media or plastic pot scrubbers. The only alternatives here for K1 are plastic straws cut up into quarter inches sections. Cut up gray (fine) or blue (somewhat fine) Matala pads or uncut straws can be use in place of pot scrubbers. Foam won’t work unless it is cut to the perfect size and shape. Polyester fibers will rapidly plug so that can’t be used. Media that do little for biofiltration in these small filters include  Matrix, Biohome, bio-balls, lava rock, or any ceramic media (ceramic rings, ceramic balls).

Static Media DIY Wide Mouth Filters.

There are three designs which will work about equally well for wide mouthed static media bottle filters. One is air operated and two are pump operated.

Design #1

The air operated design above can use any wide mouthed bottle design, such as these plastic jars found on Amazon.

These plastic bottle can be found in 8 ounce, 16 ounce, 32 ounce and 128 ounce sizes. Many other types of containers can be used with just a little bit of imagination. Note the screw on top can either be at the top or at the bottom of the design above, it makes little difference.

Here is another wide mouthed design (can also be simply a cut off water bottle or almost ANY container):

Design #2

Design #3

Still another obvious variation is simply:

All these variations look best with black paint on the outside of the bottle or jar. All these variations will work the best if the flow goes through the filter media first, then gets pulled through the pump. This filters out debris that could plug the pump.

Water Bottle Filters

The following two static designs use simple water bottles and electric pumps:

Design #4

The K1 media in this design is NOT fluidized. It will pack down around the top of the container. For this static filter any K1 will do although micro K1 is preferred. The biggest problem with this filter is getting small quantities of K1 media. If one can find it in small quantities the price is just outrageous.

Design #5

The biggest problem with this filter is getting the pot scrubbers into the bottle. Note that pot scrubbers can be easily disassembled, cut up, and simply stuffed into the bottle in small rolls or pieces. Or one can use a wide mouth bottle, leaving the top on the bottle.

Capacity of Static Media Bottle Filters

All five of the filters above have the same capacity as far as the number of fish they can filter. If a 16 oz (1 pint, 1/2 liter, 29 cubic inches) container is used this is the number of fish which can be filtered and give crystal clear, very healthy water (100 square feet of filter area per pound of fish):

Fish Length	# of Fish
1 inch	20
1.5 inches	7
2 inches	3
2.5 inches	2
3 inches	1
Very Healthty Fish

Static DIY Crystal Clear Filter Capacity

If one is willing to accept some cloudiness to the water and fish which are in reasonably good health (20 square feet of filter surface area per pound of fish), one can stock at the level below with these three filters. I do recommend one go up to this level slowly over six months or so. Do not clean these filters unless they plug up. Note that these charts are independent of the size of the aquarium.

Fish Length	# of Fish
1 inch	100
1.5 inches	33
2 inches	14
2.5 inches	7
3 inches	5
Reasonably Healthty Fish

Static DIY Reasonable Filter Capacity

These numbers are ONLY for small half liter bottles. Obviously if the container is a two liter water bottle, quadruple these numbers.

Fluidized Bed Bottle Filter Designs

These designs have pumps which force the water through a micro K1 fluidized bed. This is important. One must get flow THROUGH the bottle. There are fluidized bed bottle filters that Joey or Cory talk about which use only air to get the micro K1 circulating. These filters have very little flow THROUGH them and are thus very poor filters.

We have come up with some designs that will work as the flow is through the filter. The easiest way to make this filter is to simply add a small fountain pump to either Joey or Cory’s designs. Simple. Easy

Design #6

Again, it is best if the flow is out of the bottle and pulled into the pump. This way large particles are broken up before they reach the pump.

Design #7

Below is a design for a water bottle fluidized bed micro K1. This filter aerates the water well but it is noisy. If the bottle is 16 ounces or less micro K1 is the only media which will work. Getting the K1 to fluidizes takes patience, like four to eight weeks before it starts moving.

Here is another fluidized design.

Design #8

This design does not have the aeration of the first fluidized bed bottle filter but it is quieter. Sometimes the K1 just refuses to properly fluidize. Adding a short length of tubing at the bottom hole can help by creating a jet flow. Again, if the bottle is 16 ounces or less micro K1 is the only media which will work.

All three of the fluidized bed micro K1 filters end up being roughly twice the filter of the above static designs on a cubic inch basis if one can get the micro K1 circulating.

Under Substrate Pipe Filter

In this design a small fountain pump pulls water out of a two inch diameter PVC pipe with two drilled end caps. The pipe is stuffed with as many pot scrubbers as one can force in. The pipe is buried in the substrate at the back of the aquarium.

Design #9

This “under substrate pipe filter” is a great design for a small planted aquarium. The pipe can be hidden under the gravel at the back of the tank. The pipe can also be painted to blend in with the sand or gravel. I recommend to just force the caps on with some pressure and then leave the assembly unglued. This way one can take the pipe apart and clean it every year or two.

Note this can easily be two pipes lying parallel or one pipe which snakes around the aquarium. This design is especially attractive for a Walstad aquarium as it is very low flow and will not add the dreaded aeration, the enemy of any planted aquarium.

Another version of this design uses plastic straws instead of pot scrubbers. Note straws are very expensive if purchased over the web via something like Amazon. Amazon hates shipping all that air. But I found some very cheap in my local Dollar Store. The straws work quite well. Micro K1 will also work in the pipe.

Design #10

These pipe filters are surprising in how much they can handle. If one puts this into a 20 gallon the pipe can be 20 inches long. If one makes the pipe 2 inch diameter the volume comes out to be about 60 cubic inches. This is twice the volume of the 16 ounces bottle filter designs above. As a result this filter can do twice the fish numbers of the above 16 ounce static media bottle filters, equal to the 16 ounce fluidized bed filter bottles.

This pipe filter can be easily completely and totally hidden even in a very small aquarium. This makes it very attractive for something like a small beta tank or any nano aquarium. Note that a 1.5 inch pipe diameter gives about half the capacity of a 2 inch pipe.

It is important in all the above designs using fountain pumps have the direction of flow to be pulling the water through the media into the pump. This filters out large particles and prevents fouling of the pump.

Pipe Under Substrate Filter

This “under the substrate” filter is a very attractive option for ANY aquarium with any type of substrate. One takes a series of 1½ inch PVC pipes, fills them with media, caps them and then connects them with small flexible tubing. One then adds a small fountain pump which pulls the water through the filter.

The capacity of this arrangement is huge. And other than the small pump it can be all out of sight in the aquarium under the substrate. This is the first iteration:

Design #11

In a 20 Gallon Aquarium this will be three 16 inch sections and four 20 inch sections. This gives an astounding 226 cubic inches of filter tucked out of sight.

The capacity of this filter for a 20 square feet per pound of fish filtration in a 20 gallon aquarium (i.e. decent filtration with “dull” water) is as follows:

Fish Length	# of Fish
1 inch	500
1.5 inches	165
2 inches	70
2.5 inches	35
3 inches	25
Reasonably Healthy Fish

DIY Pipe Under Sand 20 square feet per pound of fish Filter Capacity

More importantly, the capacity for a 100 square feet per pound of fish filtration in a 20 gallon aquarium (i.e. great filtration with “crystal clear, very healthy” water) is as follows:

Fish Length	# of Fish
1 inch	100
1.5 inches	33
2 inches	14
2.5 inches	7
3 inches	5
Very Healthy Fish

DIY Pipe Under Sand 100 square feet per pound Filter Capacity

This filter is pretty amazing!

Now there are many many variations. One can split the flow as shown below.

Design #12

In a larger tank one can use two, three or even four fountain pumps with associated piping, hidden behind and under rocks or logs.

Pipe-on-Back-Wall Filter

This is a version of the filter above. It differs in that instead of being placed under the substrate it is placed along the back wall of the aquarium.

The capacity of this filter for just a little more than the two pipe designs above. Here is the basic layout:

Design #13

This assembly requires some skill with a saw. The fourteen tees that make up the framework assembly need to have the two wings cut back to nothing in a very straight and true manner. This is the cutting involved:

These tees need to then be assembled with very short (one quarter inch long) pieces of one and one half inch pipe.

Note that the one and one half inch tees can be replaced with three quarter inch tees and 14 reducer pieces. The 14 reducers go from one and one half inch pipe down to three quarter inch pipes and tees. This makes the assembly much easier to make but slightly more expensive. This is a schematic of this type of design:

Design #14

Obviously everything needs to be filled with media before it is assembled. And micro K1 will require some pot scrubbers at the entrance and exit to prevent the micro from exiting when the assembly is flushed.

The entire assembly needs to be painted black (or made of black PVC). It becomes virtually invisible against a black background. Note that it is very important the whole assembly have all its joint surfaces sanded and primed before using the PVC adhesive. It is very frustrating for the whole thing to just fall apart because the joints were not properly prepared. Also prime the entire surface before painting it if you want the paint to stick.

Altogether this is a very useful low cost filter design.

It is important in all the above designs using fountain pumps have the direction of flow to be pulling the water through the media into the pump. This filters out large particles and prevents fouling of the pump.

Variations on a Theme

There are many types of containers out there that can be made into static filters with pot scrubbers, micro K1 or straws. It is simply changing the type of container in most of the above designs. One such container is below:

Because this container is square it has a greater capacity. It is a low profile 2.4 inches by 2.4 inches. This container can be used for most of the designs above. If one takes the container and drills holes in the base, you can epoxy two or even three or four together to makes versions of the pipe filters.

Here is a simple version of a milk carton filter:

Design #15

This small filter can be painted black, dark brown or even camouflage. Then just put it in the lower back of any aquarium. It can be placed either vertical or horizontal. This will give 32 ounces, 1 pint or 1 liter of static media. This gives a fish capacity of twice the level of the first two charts above. There is no aeration and very little water movement making this a great filter for a Hau, Walstad, low tech or hybrid planted aquarium.

The Betta Filter

In the article on bettas we show a filter that will give good aeration with little water movement. This is the design:

Design #16

Probably 80% of the extra pot scrubber biofiltration will be in the green pot scrubbers. But probably very roughly 20% of the biofiltration will be in the red, yellow, and blue pot scrubbers. More important, easily 80% of the aeration will take place in the red, yellow, and blue pot scrubbers.

This all points out that there are a million ways to do this. I gave you sixteen designs that I came up with but anyone with some imagination will find many more.

A Pump Box

The small fountain pump above tends, for some enigmatic reason, to be difficult to find at times. There is another far more common design with an inlet that is an open grill. This pump requires some rework. An open grill inlet will plug with debris very frequently and need some provision to screen the debris out.

One can wrap them in foam but that is ugly and, quite honestly, doesn’t work very well. A better choice is to enclose the pump in a plastic container. In this manner the water inlet can be though the entire mass of filter media before it hits the pump, reducing fouling considerably.

This assembly can then be used in place of the fountain pump illustrated above. This is a pump design for those who cannot get the other fountain pump design.