Pond Boss Forums GENERAL QUESTIONS Pond Boss RAS 2.0 Part 4 The Siphon, Pump, & Clarifier

The clarifier above is a mechanical filter that acts as strainer that removes two types of solids: settleable and suspended. These are composed of fish waste, uneaten feed, and dead bacteria floc. The center drain covered earlier removes primarily settleable solids. The siphon that feeds into the clarifier barrel carries in the above waste to be trapped in the garden netting. With my DIY system you are removing both settleable and suspended solids just like the larger more expensive systems.

The clarifier above is one type of mechanical filter, but there are many ways to remove solids. It's important to remove solids because they uses oxygen as it decomposes and it can be a reservoir for pathogens. As it decomposes it produces hydrogen sulfide which is harmful to fish. The best filters and systems remove solids almost as soon as they are produced. A big no no in a tank or koi pond situation is to add stone to the bottom of the vessel. Uneaten feed and waste gets trapped in the crevices and is difficult to remove.

A way to remove settleable solids that will sink, if the water is still enough, is a settling tank and it's known as sedimentation. It's just a tank that the water flows into that has a lot of surface area vs. depth to slow the flow. Many settling tanks have baffles or tubes (tube settler) to slow the water down in various configurations. The disadvantage is the floor space they need to occupy vs. other types of filters.

Here's a sedimentation tank used in aquaculture:




There's also something calls a swirl filter. This is a DIY version:




An even better settling device than the swirl settler is a radial flow settler. Here's a DIY version of that:


Another way to remove solids is via a sieve filter. It's very common on koi ponds. A sieve filter has a special type of screening pattern that allows the water go through, but the solids over a certain micron size are stopped by the sieve screen and slide down to a drain. Normal screen can be used, but it will usually plug up on a regular basis. The sieve screen is usually, but not always bent in a parabolic bend to facilitate self cleaning and efficiency.

Here is a cut away of a commercially available sieve filter for koi ponds.



Here's a replacement screen for one I recently bought used at much reduced price, and will use to make my own DIY sieve filter. I can easily build something that retails for over a grand in price.



In high end koi ponds where the user can afford it, the sieve filter is followed by a rotating drum filter. These clean the water even further. Prices start at about $3000.00 dollars for a good one for a koi pond, and much bigger ones used in aquaculture can easily run ten times that.



There are lots of types of mechanical filters out there. Sand Filters, Bead filters, vortex filters, to mention a few more. But a good one removes the solids out of the water stream ASAP, and is separate from the biological filter. A biofilter that clogs with solids is not as effective as one where the solids are removed first, and in fact may cause problems for higher fish loads. The idea is to remove as many solids as you can before going to the biofilter which removes nitrogen wastes.

The following DIY sand and gravel filter is known as polishing filter. That is, once the water is filtered through it, it's pretty much gin clear. However if it's not preceded by a filter that removes coarser solids, it quickly plugs up and has to be constantly flushed. Same goes for trying to use a swimming pool filter for aquaculture. A sand filters preceded by a sieve filter works well.

http://www.koiphen.com/forums/showthread.php?68132-Birdman-s-Sand-Gravel-Filter

Here is a chart showing micron size and types of filters that can handle those sizes.


Believe the clarifier tank covered earlier in the thread with the netting, approaches the efficiency of an expensive rotating drum filter according to Steven VanGorder, the author of Small Scale Aquacultrue, however, it's more labor intensive to clean it. The rotating drum filter takes care of itself even with automatic or timed cleaning of the screen via high pressure jets.