All About Aquaculture Filtration

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If you haven't read our story yet, it will give you some background on our journey. When it comes to filtration, we've spent more than ten years trying them all in real-world backyard tilapia and catfish farming. We've spent thousands on filtration and media. If we were to place a value on our own time for maintenance, you could even say that we've spent more than a hundred thousand for our "education". We went down the filtration rabbit-hole trying to make tilapia farming more enjoyable for ourselves and now we are sharing our accumulated knowledge with you so that you won't follow in our footsteps.

For the most part, raising food fish is pretty easy. It's the filter maintenance tasks that take all the enjoyment out of it. Constantly cleaning media, getting splashes of fish poop on your skin, in your hair, on your clothes. Dealing with broken or stuck pump impellers that quickly turn into bloated mag drive housings that seize pumps and offer eye-opening electrical shocks. Internet DIY filtration "solutions" that solve one problem while creating new ones. Not to mention all of the ways that the fish themselves will defeat filters. Tilapia are powerful underwater and can knock off just about every canister suction tube and over-the-back filter intake on the market. And if you're raising fry, a poorly conceived filter can ruin their day pretty fast as well. We can go on and on, but you get the idea.

So the hope of this page is to share the most important things about filtration with you. If at any point we teach you one thing that you didn't know, then we've done our job. So without further ado, here's everything that you should consider when thinking about filtration. 

Categories of filters

All aquaculture and aquarium filters fall into one of two types:

1. Waste traps

2. Waste removers

We may as well get waste removers out of the way right off the bat. Waste removers do exactly that. They remove wastes from the water in which the fish are swimming. The only waste remover that isn't just you standing there with a net scooping up fish poop is a Drum Filter.  And while there are some small drum filters that are marketed to koi pond owners, anything coming close to meeting the requirements of tilapia is going to cost in the tens of thousands of dollars. Heres an example of a proper drum filter and here's an example of an "inexpensive" (only $2,900) drum filter for koi that would quickly become overwhelmed by the volume of waste created by tilapia. So considering the price point for a drum filter that would be adequate for even 100 tilapia, we will end the discussion of waste removers here. What we are left with is waste traps.

Everything that isn't a drum filter (or you standing there with a net) is a waste trap. As the name implies, they trap wastes in the same water in which the fish are swimming. Examples of waste traps are too numerous to count, but generally speaking they encompass everything from hang-on-the-back type aquarium filters to canister filters, from in-the-tank filters to air powered sponge filters, from horizontal pond filters to bead filters. Hiding the waste from view doesn't mean a thing, no matter how far removed from sight. If the water repeatedly passes through the trapped waste and is then returned to the fish, that ladies and gentlemen is a waste trap.

Note that we are only discussing filtration systems used in live fish systems. Other filtration methods, such as belt filters, centrifuges or filters that utilize diatoms or chemicals are not and should not be used for Aquaculture.

What is fish waste?

So let's briefly discuss what "wastes" we're talking about. With tilapia farming it's mostly fish poop and uneaten feed. Tilapia are the second-fastest growing freshwater fish on the planet. That kind of metabolism requires a lot of food in a short amount of time.  Think about this.  Just 100 tilapia requires 4.5 pounds of starter feed, 6.5 pounds of grower feed and 88 pounds of finishing feed. Thats 99 pounds of fish meal and grains dumped into your pond for every 100 fish. Whether that food is removed in the form of fish poop or uneaten feed, all 99 pounds needs to be trapped and subsequently removed from the water when you service the filter. But it's not just fish poop and uneaten feed.

You also need to remove dissolved solids, bacteria and fish mucus or slime. This is where all filters, even the most sophisticated drum filters, lose the fight and eventually need servicing. These microscopic things stick to everything, even rotating drums and bio wheels. No filter escapes this, no matter how creative or well designed. And while we're in the subject, a poorly designed filter will plug with this stuff within hours, not days, even from a relatively clean tilapia tank or pond. The only salvation is a filter designed to be serviced very quickly and hold a relatively high volume of wastes. Which brings us to the next filtration subject.

Holding capacity

Most filter manufactures play a little word game by recommending the size of tank in which a particular filter is to be used. The size of the filter has absolutely nothing to do with the volume of water. Think about this. If you put one fish in a swimming pool, there is no way on earth that one fish is going to make enough poop to need a filter system capable of 80,000 gallons of water. But because larger aquariums are far more expensive than smaller ones, they capitalize on the customers with deeper pockets and base their filter (more expensive) recommendations on water volume, instead of holding capacity. Of course there are also those who base their recommendations on biomass, but they are playing a different marketing game.

Some filter manufacturers want you to size a filter based on "inches of fish" or "numbers of fish" without regard to the type of fish. Think about those little plastic jars with 2 ounces of tropical flake food for angel fish or other ornamental fish.  Just about any filter can trap 2 ounces of digested and uneaten feed and tiny amount biological matter. So stating that their filter can be used with "x" number of fish or "x" inches of fish is only true with certain fish, but not aqua-cultured fish like tilapia or catfish. It would be more honest if filter manufacturers simply stated the weight of waste that a particular filter could trap before it required servicing. But sadly, there are even filters designed to continue flowing, even when they are full of s**t.

Hang-on-the-back filters are one type that are designed to appear functional, even when they are aren't filtering at all. When these are full of waste, the water simply passes over the top of the filter giving the illusion that it's still doing its job. Horizontal pond filters are designed in the same fashion. When their Matala mats are full, the water simply diverts around the filter media. These devious filter designs allow the once-trapped waste to dissolve into the water making them nearly unrecoverable and they need to be constantly inspected by the fish keeper. The need for a positive indication that a filter needs servicing cannot be overstated.

Rather than wow us with irrelevant tank sizes and fish counts, it would be far more informative if they just told us how mush fish waste their filter can trap before it needs servicing. In fact, the only measure of an aquaculture filter is its holding capacity. However, more holding capacity isn't necessarily better.  A holding capacity that is too high will allow earlier trapped wastes to begin to decompose into nearly microscopic particles that will break away and pass through the filter media making them nearly impossible to trap. In addition, holding wastes in a filter media for too long encourages the growth of harmful and oxygen-consuming bacteria.

It's important to find a filtration solution that holds as much waste as possible before the held waste decomposes and provides a visible indication when the filter media is reaching its holding capacity.

Poop chewers

Any filtration system that passes wastes through a water pump impeller before the filter media is a "poop chewer". Poop chewers are a biological nightmare for tilapia and catfish farmers or any food-fish farmer for that matter. Poop chewers turn easy-to-trap particles into dissolved particles that cannot be trapped. The vast majority of filters on the market today are poop chewers. Even some expensive canister type filters pass wastes through a pump impeller before the filter material. How does that even make sense.

Many poop chewer manufacturers use proprietary filter media containing activated carbon to help remove the dissolved solid particles that their own filter helped to create. Which, you guessed it, brings us to our next topic.

Proprietary filter media

Filter manufacturers want you to join their little club of dedicated filter media buyers. Ever notice how a new printer is cheaper than the ink cartridges? The same goes for filters. Sure they make a little money when they sell you the filtration, but the big bucks are made month after month when you buy replacement media. Every manufacturer has their own patented proprietary design and a lawyer to keep low-cost alternatives away. Sure, some media can be rinsed and re-used to some degree, but it's designed to self-destruct eventually. It gets no better with canister filters either.

The sponges used in some canister filters are made from a material that begins to get brittle and fall apart over short period of time. This is not an accident. To find out if the sponge filters that come with a particular canister filter will fall apart over time, one only has to see if they offer replacement sponges for their answer. Not to say that this is all bad, there is something to be said for filter media that can be serviced and reused.

Ease of service

By now it should be obvious that all fish filters regardless of type, need to be serviced at some interval. The time between servicing has a lot to do with the volume of trapped solids in the media as well as the overall tolerance for filth of the fish keeper. The question is, how long does it take to service the filter?  With horizontal pond filters for example, every Matala mat needs to be removed and pressure washed. This takes time. Even more time-consuming, canister filters need to be disassembled and cleaned by hand in a sink, not to mention all the water that drips on the floor. The lowly hang-on-the-back filter is fairly quick, but at five bucks or more per media cartridge, you're definitely paying for the speed.

Bead and sand filters can be a biological disaster to backwash and almost always release that toxic waste back into the pond when the process is completed. Not to mention the time that it takes to perform the service. Of course everything changes for the worse if you get the next type of filter.

All-in-one filters

All in one filters are those that try to do too much in one step. They usually start by passing the waste water through some sort of coarse filter media (if not the pump impeller first) then a fine filter step followed by some sort of water treatment like activated carbon. Then they pass the water thorough some sort of bio media where nitrobacter and nitrosomonas are supposed to be growing in order to convert ammonia into nitrates, but this is woefully insufficient for anything but a handful of small fish. In general, these filters are just okay, say three out of five stars.  They aren't awful, but there are far better methods that do a superior job. It would be far better to leave the bio-conversion step to another piece of equipment. But since we mentioned it, let's dive in.

Bio-conversion

This is where we are going to lose a few people. There's just so much BS on the Internet about the "need" to convert ammonia into nitrate. But if they are willing to understand some actual scientific facts, we can deprogram their brainwashed minds. So here goes nothing.

Nitrates only appear because nitrifying bacteria (nitrobacter and nitrosomonas) "eat" ammonia. Ammonia only comes from fish pee and fish respiration, not fish poop. Fish poop is a useless pollutant. No, if you have an aquaponics system, your system does not benefit from fish poop (but more on that later). Bio conversion occurs on every surface of your tank or pond because that's where the nitrifying bacteria live. The only purpose of bio media is to provide more surface area for nitrifying bacteria to live. The worst possible place for nitrifying bacteria to live is in an area of high water flow (sorry fluidized media people, but it's measurably true)

The best possible way to convert ammonia into nitrates is with slow moving water past a stationary media for surface area such as in an aquaponics sump, again, proven true regardless of Internet forum "experts", But here's the kicker, none of this even matters if you don't have aquaponics. Why? Because ammonia isn't toxic below a pH of 8.0! Have a look at any ammonia test kit or strips. Notice that it reads NH3 and NH4. This is because ammonia tests can only test for total ammonia, the benign and the bad. If you keep your pH at 8.0 and below, no amount of ammonia is going to be toxic to fish. Now let's  go back and talk briefly about fish poop in aquaponics systems.

Fish poop is useless in Aquaponics

Fish poop consists of digested and undigested food, gut bacteria and mucus, none of which are beneficial to plants in an aquaponics system. In order to be beneficial to plants, the fish poop needs to be composted like any other animal fecal material. This is why composting exists. This is why farmers don't plant seeds in freshly laid manure. This is why you don't put raw sewage in your garden. Adding fish wastes to aquaponics plants introduces oxygen-consuming bacteria that can starve plant roots. But wait you say, what about mineralization?

Mineralization is the "composting process" that happens underwater in an aquaponic system. The problem is that it happens very slowly, on an almost geologic timeline. By the time that mineralization occurs, the fish that made the poop are long gone. On large tilapia farms, the fish poop is removed by drum filters and moved to a conveyor belt that deposits the fish poop into a pile on the ground. The poop is then composted using traditional methods and used like any other. The bottom line, it's just not worth having the oxygen-starving bacteria in your grow beds for some imaginary poop benefit remove it from your water, regardless of the style of tilapia farming.

So what is the best filter method?

Well as if you didn't see this one coming, we believe that we've created the perfect filter for backyard aquaculture, the Home Tilapia Pro. It traps fish waste and has a relatively high holding capacity. It doesn't run unfiltered waste water through the pump to be chewed up. It doesn't need proprietary filter media. In fact we don't even sell filter media, you use whatever you want. It only takes seconds to change your filter media and there's nothing to rinse or reuse. It allows you to add custom water treatments like activated carbon to control dissolved particles and control phenols (stinky stuff) or even clinoptilolite to absorb unwanted water chemistry. Plus it can preform other non-filter related duties such as aeration and water circulation. It's what we had been searching for over ten years to find and finally decided to make ourselves.