Uneaten food and organic waste will accumulate and decay in the gravel on the bottom of the aquarium. If it is not removed regularly, the chemical balance of the water will be affected, and could abnormally affect your newts' health and behaviour. Filters are designed to properly remove this waste from the aquarium, and therefore, maintain the chemical balance of the water, making for healthier living conditions for the newts. However, regular maintenance is still required and filtration systems should never be used to eliminate this necessity in any way!

CHOOSING A FILTER:

Terrariums do not require filtration. However aquariums do require filtration in order to maintain clean, safe water also reducing the need for regular water changes.

There are a variety of filter systems available to choose from, however most are usable only for aquariums which contain full bodies of water. Keep in mind that most filters are designed for this purpose.  However, some filters can be adapted for different water levels by either purchasing adaptors or longer hoses.

NOTE: It is important to be sure the filter outflow is not too strong, as most newts are not strong swimmers. Newts which try to swim against strong currents will cause considerable stress and will also weaken them fairly quickly. Keep in mind that all filters have outflow, which produces a current. The key is to attempt to reduce the current as much as possible. This can be accomplished by diverting the outflow to another section of the aquarium, block or disperse the outflow using plants or rocks to break the current, or attach plastic tubing to the output adapter, drill a series of small holes throughout, and cap off the far end. The outflow is part of the filtration system, what drives it, and circulates the water. I recommend purchasing a filter which produces less output. That is the next size smaller than is normally recommended for your aquarium dimensions, as most filters are designed for full bodies of water, whereas newts are housed in a reduced body of water. Regardless of the filtration system used, be sure to allow the outflow of the unit to agitate the surface of the water. Lack of adequate surface agitation can cause stagnant water as well as harmless, but unsightly scum to form.

NOTE: While adding a second filter in a small aquarium would be overkill, in a larger aquarium can be beneficial, as it greatly reduces the amount of accumulating wastes. A cleaner and safer environment is created and allows for new additions.

TYPES OF FILTRATION SYSTEMS:
Consisting of biological and mechanical filtration systems.

These are a few types which can be used for low or partial water situations.
Please keep in mind however, that the following filtration systems listed are not inclusive of all possible filters available for use in these situations, but are a general overview.  Filter systems are subject to availability and location. Therefore, some filter systems are not listed due to lack of availability in my area and without direct knowledge of the product I am unwilling to provide comment on effectiveness or performance. 

NOTE: The following is based on my observations and what has been effective or non-effective for me. The filtration system you choose should be based on your own requirements. Biological filters such as the undergravel system, require regular gravel cleanings. Without, it will become clogged, cutting down on the needed oxygen supply to the bacteria, thus hindering the overall performance. Therefore, if you are a low-maintenance person, then chances are biological filters are not for you. Mechanical filters still require gravel cleanings, but if not done as often, will not hinder the performance of the filter.

BIOLOGICAL:

UNDERGRAVEL FILTERS:

Consists of one or more plastic plates, depending on the size of the aquarium, which snap together and are placed onto the bottom of the aquarium. Plastic return tubes are attached to the plate and can be cut to accommodate any water level. Gravel is then placed on top of the plates. Beneficial bacteria will develop below the plates and throughout the gravel, essentially filtering the entire tank. Initially, bacteria will not develop on its own. Either using aged water from an already established aquarium in order to jump-start the new colony, or by using Cycle Bacterial Supplement. (See below) Cycle is fairly expensive but is laboratory tested safe and effective when used regularly. Jump-starting the colony is inexpensive and effective, but can also be risky. Using water from unsatisfactory or an unreliable source can pose potential health problems, as diseases may be introduced. Once established, the bacteria work to break down harmful organic waste and detoxify ammonia. Water is circulated throughout the entire plate, and is drawn down through the gravel and returned up through the return tubes. The constant supply of oxygen circulating through the plates will nourish the bacteria. Unlike other filtration systems, the Undergravel is a permanent system, therefore do not remove the plates. Cleaning is done via a gravel vacuum unit and the plates should not be lifted. Filtration can be improved by adding either an Air Pump or Powerhead to the return tubes.

Air pumps incorporated with the Undergravel System are used mainly for increased air circulation and added oxygen content. Due to the limited circulation, water can become stagnant quickly. These are less effective and are quite noisy. If needed to operate more than one accessory from a single pump, purchase an air control valve, which will divert the air as required.

Air pump and splitter.

The most effective method of improving filtration is to add a Powerhead onto the return tube or tubes. These operate quietly and effectively with the Undergravel System. Powerheads greatly increase circulation, thus preventing stagnant water. Each unit has a valve which controls, and allows you to adjust the outflow. These can be positioned anywhere in the aquarium, using either the supplied bracket or suction cups, which will allow you to position the Powerhead deeper into the aquarium, and can easily be removed by sliding them off the bracket. Powerhead units are sealed, and therefore water cannot penetrate into the motor, and protects against shock. A hose can easily be attached onto the exhaust shaft in order to provide water return elsewhere in the aquarium.

NOTE: Air pumps, powerheads and common aerators are not filtration systems and thus will not filter water on their own. These are merely types of pumps available which aid your filtration unit; oxygenating the water, increasing air and water circulation, as well the performance and efficiency of your filter system. These pumps must be used in-conjunction with an actual filtration system.
 

SPONGE FILTERS:

Depending on the size of aquarium, either a single or double Sponge Filter can be used. This filtration system relies solely on an air-driven system and an air pump must be used in conjunction with it, increasing oxygen content, which is unnecessary for newts. These filters produce an abundance of air bubbles which the newts can ingest. Although these can be expelled in a few days, it can cause the newts to float and will have difficulty submerging. To prevent this, either kink the hose with a clothes pin or purchase an air control valve to reduce the amount of bubbles.

Beneficial bacteria will grow on the sponges and assist in transforming harmful wastes into a less harmful substance. Sponge filters prove effective against ammonia, but organic wastes and uneaten food will remain and decay on the bottom of the aquarium, as there is no filter apparatus to draw this debris into the sponges. Vacuuming the gravel will be required more often. The filter is easily cleaned by removing the sponges and rinsing with cool water. Never use hot or cold water, as this destroy the beneficial bacteria accumulating in the foam. Cycle is suggested to be used on a regular basis with these filters.
 

CYCLE BACTERIAL SUPPLEMENT:

CYCLE is a laboratory tested, biological method used to destroy harmful ammonia, and other toxins which in high concentrations can cause illness or death to your newts. CYCLE is in liquid form and contains huge quantities of the beneficial bacteria, and once added instantly begins to populate or strengthen existing populations, creating safer living conditions. CYCLE may be added regularly according to the directions on the bottle to ensure a constant and healthy bacteria colony. Regardless of the type of filter system being used, the filter should be kept running at all times, except for only brief periods of time when necessary, as the bacteria needs a constant supply of oxygen to survive. After several months when your tank has matured, the CYCLE can be discontinued as the bacteria will be self-sustaining and reproduce on its own.

Cycle Bacterial Supplement.
 

MECHANICAL:
Consisting of internal and external filtration systems.

When replacing filter media, be sure to add a small amount of the old media with the new, in order to maintain any established bacteria level and to repopulate the new.

INTERNAL FILTERS: These are completely submersible, useable in all water level situations and can easily be placed anywhere in the aquarium.

FLUVAL FILTERS:

Water is drawn through either a foam or carbon impregnated pad. Recent models incorporate a stacked media system to further enhance filtration. Media must be replaced regularly or will greatly hinder the performance of the filter and quickly affect the water conditions. Be aware, frequent media replacements can become expensive but are necessary. Outflow can be quite strong, producing rapid currents which can create a stressful situation for the newts. To prevent this problem, purchase models with an adjustable outflow or which come with appropriate attachments to accomplish this. Filter effectiveness tends to be limited with these models without proper apparatus to draw wastes into the filter.
 

BOX OR CORNER FILTERS:

Simple filtration system in which filter media is stacked inside and water is drawn through, in order for purification. Media mechanically remove debris from the water, while some bacteria can grow on the filter media to assist in chemically breaking down wastes and detoxifying ammonia. Although quite inexpensive, these filters do have some limitations. Their bulky size takes up a fair amount of space inside the aquarium and is quite unsightly. Quite minor considering an attractive plant will easily conceal the filter. The unit is operated via an external air pump, which can be quite noisy. Also, keep in mind that the newts can become trapped between the filter and the aquarium walls. This can be avoided by placing a foam pad in-between and gathering the gravel underneath to hold in place. The main disadvantage is the fact that their use is restricted to small aquariums due to their size and very limited water movement. Wastes accumulate quickly and the water becomes stagnant due to the lack of adequate circulation. As a result, these filter systems are best suited for temporary use only, and are not recommended for permanent use.

There are basically two filter media which are used:

Filter floss: Also sold as filter cotton or in cartridge forms, this is a necessary media. Inexpensive and provides the mechanical filtration by straining debris from the water.

Activated Carbon: Provides the chemical filtration. This essential media removes odours and ammonia from the water. The high quality carbon is more expensive, however it is more effective and lasts longer.

Common box or corner filter unit.

SAND SHARK:

A fairly inexpensive unit which utilizes a carbon/zeolite filter cartridge, effectively neutralizing ammonia and odours along with any other harmful substance. Equipped with a built-in adjustable outflow and control valves. Again media must be replaced on a regular basis for best performance. Replacement cartridges are readily available, sold in convenient packs.
 

DUETTO:

Similar to the Shark systems. The Duetto is flat and the outtake shaft can be rotated to expel in many directions. Thus this unique feature allows this model to be used in shallower waters than the Shark or other submersibles. Also, rotating the outtake provides maximum agitation to prevent stagnant water and can create a stream environment. It is deemed the most versatile of all submersible internals.
 

EXTERNAL FILTERS:

"WATERFALL" FILTERS:

Models such as AquaClear and Dynaflo Power filters, which are designed to attach onto the back of the aquarium. Using a large tube which extends into the aquarium, it draws the water, forcing it through a layered filtration system, and returns as a waterfall system. These filters are effective in filtering organic waste and removing ammonia, but are not very useful in low water situations, such as those for aquatic newts. The less water in the aquarium, the farther the water has to fall. This can be quite noisy and makes for harder maintenance, as the water will splash onto the glass and cause a water film to form. It also creates a strong current when it hits the surface. Newts can also become trapped behind the filter apparatus and climb the tubes to escape. Adding a section of clean foam between the glass and the tubes, and sealing with aquarium silicone, can prevent this however.
 

FLUVAL CANISTERS:

Sold in a variety of models. Again, I suggest purchasing the next size smaller model than what is designed for your aquarium size. These systems incorporate the best media technology available today. Models can hold from 4 to 8 different media types and allow you to choose the appropriate media for your situation. Minimal space is used inside the aquarium for the filter apparatus. The canister is placed below the aquarium which makes it easier to access for maintenance.  If the hoses are not long enough, adaptors can be purchased. The intake tube extends into the aquarium, draws the water and forces it through the many media layers. It returns into the tank purified. This is a filter system that can be used to achieve a waterfall. A highly effective filter system, however there are 2 minor disadvantages I have encountered. The hose apparatus must hang over the back of the tank, causing issues where the cover is concerned. To prevent escapes, the cover must be modified for the apparatus. Secondly, periodic cleaning of the hoses is required. If using a cap on the tank or if the tank is in an awkward location, this process can become more difficult.

Fluval 204 model, external canister.