Pond Filters

Filtration is the heart of successful pond management. There are many different type of filters available on the market. Ensuring that your pond water is safe for fish is essential to maintaining a happy and healthy pond environment and reducing the risk of disease.

Basics of how filter works

Purpose of filters are NOT to physically keep water clean. You achieve this with all filters to some extent as a bonus. Filters are used to remove TOXINS produced by fish and other decaying wastes. Those toxins are INVISIBLE and crystal clear water does NOT mean water is safe for fish. Helpful bacteria settles in filter media over a period of time. These helpful bacteria breaks down those toxins and make water safe for fish. Water can be murky and looking dirty yet safe for fish if you have an active filter, meaning a filter which is running for months and have plenty of helpful bacteria. You need to keep water running through filter 24/7 for them helpful bacteria to survive and keep doing their job. You never clean filter media with tap water which may have chlorine (chlorine kills helpful/friendly bacteria). Always use same pond water to do a moderate clean of filter. Those helpful bacteria’s are invisible and die easily when out of water for too long (can be minutes in dry sunny condition) or no water passing through filter, half an hour is too long for them to survive in hot climate without running/oxygenated water.

” Without helpful/ friendly bacteria ( nitrifying bacteria ), a filter is DEAD”

These helpful bacteria occurs naturally but it is a good idea to introduce them to all new and sometime existing pond/filters.


Source of carbonate is essential for all pond unless you add them regular. Several carbonate molecules get used with each oxygen molecule to breakdown ammonia into nitrite. Amount of carbonate present in water is measured by testing KH from your water test kit. Koi guru recommends a KH value of 7 or 8. When KH is good your PH will be stable., ammonia will stay close to zero.

Calcite rock (non crystalline/brittle type) and cheap garden centre limestone or oyster shells are very effective but you will need a good amount as they dissolve very slowly. “KH – buffer up” from NTlabs is one of the best. Temporary alternative can be bicarbonate of soda.

Filtration is the heart of fish pond, carbonate and oxygen is the heart of filter

I have few multichambered fibreglass filters that I use with flocor, alfagrog, limestone and calcite rock (non crystalline/ brittle type) .

I use flocor in first two chambers, alfagrog (E40 size, smaller size will get clogged and hard to clean while largers can be cleaned by simply pouring pond water over them) in next two chambers, limestone (too much small size limestone will clogg filter) in next and finally calcite rock (non crystalline/brittle type) in the last chamber. Flocor is light and can be stirred & cleaned frequently. It makes this type of arrangement easy to maintain and are relatively clog free.

** I always supply extra oxygen with air stones etc on all multichambered filters when temperature is above 12 ish Celsius**

I have used above example as many hobbyist opt for better filters ( like nexus, bakki showers, drum filters etc) with higher price tags but forget to add minerals on regular basis. Multi chambered filters can be perfect for low cost/maintenance filtration.

Types of filter media among many, available to choose from and perfect for DIY filters.

Here are few example of different types of filter. Some can be modified and rearrange filter media for more effective filtration and easy maintenance.

Drum filters

Legendary Nexus

Bakki showers

Pressure filters

Multi chambers

UV Light to control Algae

UV filters to control algae is a personal preference but if you get dense pea green soup colour water then UV filter may become necessary to avoid fish loses. I only use UV with nexus setup while my multichambered filter setups are fine without UV. Ponds with slight green colour water is much better for fish than crystal clear water. You will need to replace UV bulb at certain intervals for effectiveness. I usually change bulbs once every two years (not 6 months as instruction, yes that’s true) .

How much algae you get will depends on many factors such as amount of sunlight, fish load, other organic debris etc. Having lots of pond plant and lower fish load is a very effective way to control algae naturally.

All new pond should have their UV filter turned OFF for first few weeks at least. This way nitrifying bacteria can develop quickly in the echo system. UV filter/light will kill bacteria, good or bad.

1 thought on “Pond Filters”

Leave a Comment

Your email address will not be published. Required fields are marked *

Shopping Cart