Part 08: Filtration, Reactors, Algae Scrubbers, & UV Sterilizers

Table of Contents

I) Introduction

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II) Filtration

In the saltwater aquarium hobby, there are the BIG 03 when it comes to filtration: mechanical, biological, and chemical.  We are going to do a quick overview of each type of filtration, and then dive more into the various media types as well. That way you will know what’s available, what we recommend, and what things you may need to purchase for your saltwater tank.

1) Mechanical Filtration

Mechanical filtration is the process of removing large pieces of matter from your tank, such as fish food, fish waste, and algae.  

The first three types of mechanical filtration all pretty much work the same:

  • sponges
  • filter floss
  • and filter socks

Water passes over each of these, and the media catches large pieces of matter, thus filtering it out. With each of these methods, you will want to replace the media every few days.  If you do not, then the decaying matter will turn into ammonia which is harmful to your livestock.

But protein skimmers work differently.  Let’s go over each method below.

a) Sponges

Brightwater Premium Foam Sponge

You don’t get much more simple than a sponge.  I use the BrightWater Sponge pictured above in my 24 gallon reef tank.  I have used many different types of sponges, but nothing beats the one from Brightwater.  It is super dense and holds together amazingly well.  I cut four pieces that fit into my overflow, and then every three days I take one out, rinse it, and replace it with a clean one.  Love these sponges.

Sponges are easy to clean, and don’t require a wash cycle and bleach like filter socks.  Sponges are not as dense as filter socks, so will likely let more organic matter through.

You could also use a filter cup with the BrightWater H-Series sponge media below.  Another great sponge option.

BrightWater H-Series Sponge Media
Filter Cup

Filter floss is hobbyist lingo for any type of polyester filter fiber.  It comes in small white strands, resembling dental floss… hence the name.

Filter floss is quite similar to a sponge, except that with a sponge you can rinse and reuse, but with floss you just throw it into the trash.

I’ve used two types of filter floss. The one on the left is more expensive by far, but it holds together better and you don’t find strands in your tank.  The one on the right is super cheap, but doesn’t hold together as well.

c) Filter Socks

7 inch white filter sock, new, lying on it's side with opening facing camera
200 Micron Felt Filter Sock

Filter socks have long been a staple in the saltwater hobby, although for some reason there is a current trend of getting rid of them.  Not exactly sure why, except that there are some hobbyists out there that over-filter their water.  But rest assured, filter socks have a proven track record of success.

In order to use a filter sock, your tank needs to have some sort of filter sock holder. Most reef tanks come with these, as do most sumps.  There are a couple different standard sizes, so just make sure you buy the right one for your setup.

200 micron felt is the standard in the hobby, but you can also purchase super fine 10 micron socks.  I don’t recommend these for beginners as they will get clogged super quickly.

d) Protein Skimmers

Believe it or not, protein skimmers are 100% a type of mechanical filtration.  But they work differently and are confusing to setup and understand for beginners.

Here’s how they work:

  • Protein skimmers create bubbles by means of a pump.  Small particles of organic matter that slip through your sponge, floss, or filter sock, are sucked into the skimmer.  These pieces of organic matter are hydrophobic, and are attracted to the bubbles.  The bubbles are then pushed upwards into a collection cup, which is then emptied from time to time.

Protein skimmers are still considered the backbone of reef tank filtration, as they can remove a lot of organic matter from the water column.

© Marine Depot

All skimmers will take a couple weeks to break in, so don’t be surprised if your new skimmer overflows constantly for a week or so.  It’s not you, it’s your skimmer.

All protein skimmers have a water depth that they operate best at, so follow the manufacturer guidelines, and put something underneath the skimmer if you need to raise it up. I like to use ceramic media plates for this, as I’m not only raising the protein skimmer up to the correct height, but I’m also adding more biological filtration which is never a bad thing!

All protein skimmers will have some sort of adjustment knob. This will slightly change the water height in the skimmer, thus giving you a wetter or dryer skimmateSkimmate is just hobbyist lingo for the brown organic matter in the collection cup. Wet skimmate means your reactor is pushing a lot of bubbles over into the cup, and is generally lighter in color.  A dry skimmate is darker in color, and is caused because less water is being pushed over into the collection cup.

Below are a couple of my favorite protein skimmers.  The one on the left is a nano skimmer meant for small tanks and usually placed in the rear filtration chamber.  The Bubble Magus on the right comes in various sizes and is great for larger tanks with a sump. Just an FYI, I own each or these!

AquaMaxx Nano Protein Skimmer
Bubble Magus Internal Protein Skimmer

2) Biological Filtration

Biological filtration is the process of cultivating various types of beneficial bacteria to consume and convert organic matter, turning it from toxic ammonia to non-toxic nitrogen gas.  Whenever we talk about the nitrogen cycle, we are talking about biological filtration.

nitrogen cycle infographic

For most saltwater hobbyists, their primary biological filter is live rock and live sand.  During the process of cycling your tank, both aerobic and anaerobic bacteria will colonize your live rock and sand, consuming ammonia and turning it into nitrogen gas. But for a whole bunch of reasons, sometimes that is just not enough. 

So if you notice your ammonia or nitrate spiking and not going down, it’s time to do something to increase the capacity of your biological filter.  There are four different ways to do this:

a) Ceramic Media

Ceramic media is highly porous and a great place for beneficial bacteria to colonize.  It comes in all types of different shapes and sizes, so really you just need to purchase the correct type for your space.  For example, if you have a smaller tank with either a HOB power filter or a rear filtration chamber, something like the ceramic balls or blocks below might be a good choice for you.

Marine Pure Bio Spheres
Brightwell BIO Blocks

But for those of you with larger tanks that have a sump, you might be better served by either the Marine Pure Bio Plate of the Brightwell Bio Brick. These work great in the refugium section of your sump, or placed vertically in between the baffles.

Marine Pure Bio Plate
Brightwell BIO Blocks

b) Biopellets

The easiest way to explain biopellets are steroids for your beneficial bacteria. Biopellets provide a dense carbon source for your beneficial bacteria to consume.  When placed into a media reactor and gently tumbled, beneficial bacteria will colonize and consume the biopellets themselves.

You don’t need to add biopellets when starting out in your reefing adventure.  But, if you notice that your nitrates are high and no matter what you do you just can’t get them down, then biopellets and a reactor may be the choice for you.

Just a couple things to consider though:

  • Once you start using biopellets, you need to monitor your nitrate levels frequently. While it is good to have low nitrates, it is not healthy for your corals to have zero nitrates.  So follow the dosing instructions, and add the correct amount.
  • You will need to top off your biopellets from time to time, as the beneficial bacteria will actually consume them for food. If you allow the volume of biopellets in your reactor to get too low, you may notice a large nitrate swing since there is no longer enough food for the beneficial bacteria.  So again, monitor your nitrate levels by testing frequently.

I really like these biopellets by Two Little Fishies below, and the AquaMaxx reactor will work well for tumbling them. You will need to purchase a small pump to power the reactor though.

c) Carbon Dosing

Carbon dosing is similar to using biopellets as you are adding a food source to your tank to encourage the growth of beneficial bacteria.

But it is different in one crucial way: Whereas biopellets encourage growth of beneficial bacteria inside the reactor, on the media itself, carbon dosing encourages that growth throughout your entire tank.

There are many different sources for carbon dosing such as vodka and sugar, but I like to use products specifically made for the reef tank. 

Again, just like with biopellets, you need to closely monitor your nitrates, and adjust the level of carbon dosing accordingly.  Also, be sure to not suddenly just stop carbon dosing.  This can lead to a catastrophic crash in the number of beneficial bacteria, and thus a quick rise in ammonia and nitrate.

d) Plastic Bioballs

These are uncommon in the saltwater hobby, just because their are more effective ways to increase your biological filtration.  These bioballs work just like their ceramic counterparts, except plastic is not nearly as porous and does not provide as much surface area for beneficial bacteria to colonize.

But on the plus side, these will last forever and are not brittle like ceramic media.

3) Chemical Filtration

There are a lot of different chemicals out there, but they all serve a similar function. Chemical filtration is the process of using some sort of chemical to remove unwanted things from the water such as phosphate, nitrate, heavy metals, smells, and colors.

In a well balanced tank, you won’t need to use chemical filtration all the time, but rather as a supplement occasionally when something gets a little out of hand.

a) Activated Carbon

Activated carbon is basically charcoal.There are few different types of activated carbon, some of which are more efficient (and more expensive) than others.  But they all do the same thing: remove heavy metals, chlorine, smell, and color. Just think of your Brita filter- it is primarily a carbon filter.

You can use carbon in either a media bag or a reactor. If you use it in a media bag, be sure to rinse the carbon first to remove all of the black dust, then place it in a high flow area of your tank where it will have the most potential to interact with your water column.

Carbon will be more effective if used in a reactor, but again you need to rinse it.  Not only that, you want to make sure you don’t tumble the carbon, because it is quite brittle and will break down into dust and spread throughout your entire tank.

The ROX 0.8 carbon on the left from Aquamaxx is pretty much the top of the line.  It is more expensive, but has been proven to be more effective in the removal of contaminants. It is also less dusty.  But to save some money your standard Aquamaxx bituminous carbon on the right will work just fine.

b) GFO (Granular Ferric Oxide)

GFO removes phosphates.  That’s pretty much it.  There are other, more natural methods of removing phosphates from your water column such as using macroalgae in a refugium or investing in an algae scrubber.  But GFO works, especially if you are battling a really bad nuisance algae outbreak.

Again, just like carbon, GFO will be most effective when used in a media reactor, but you can also use a simple media bag placed in a high flow area of your tank.

GFO is much harder that carbon, meaning you can gently tumble it in the media reactor without worrying about it breaking down. Just be sure to rinse GFO with RO/DI water before using it in your tank, or you will get a bunch of brown dust covering everything, which looks bad and is not great for your corals!

Just like with the activated carbon, GFO comes in a high capacity version, and a regular capacity.  I’d recommend just starting with the regular capacity on the bottom left because you don’t want to strip too much from the water column. A little bit of phosphate is a good thing, but zero is bad!

c) Purigen

Purigen is a highly effective synthetic product that absorbs and holds onto organic nitrogen compounds as well as proteins.  While it doesn’t remove nitrate directly, it does absorb organic materials that will lead to nitrates.

Another cool thing about Seachem’s Purigen is it can be reused by regenerating it. Check out the Seachem website for detailed instructions on how to do this.

Purigen can be used in either a media bag or a reactor, and generally can last up to 6-months before it needs to be regenerated.


III) Reactors

When I first started out in this hobby, reactors were, without a doubt, the most difficult topic for me to understand.

While there are several different types of reactors, let’s simplify things a bit.

A reactor is a container that hold media, where water passes through, thus causing the media to interact with your water column.  That’s it.  Different reactors work slightly differently, but they all share those same characteristics.  

Reactors are usually considered the most effective way to utilize filtration media, but you can also use inexpensive filter bags, so let’s start there.

1) Media Bags

Media bags come in several different sizes and styles, but they are just a mesh bag used to hold some sort of filtration media.  You can get a fine mesh bag for smaller media such as carbon and GFO, or a coarse bag for ceramic media, bioballs, or biopellets.

They are a type of passive filter, and will only be effective to the extent that a high volume of water passes through them on a regular basis every hour.  So placement of media bags is crucial for their effectiveness.

2) Carbon/GFO Reactors

The most basic type of reactor is a carbon/GFO reactor.  Simple in design, water flows down through the central tube, and then up through the media and out to your tank. 

These types of reactors are active, meaning that water is forced through the canister, thus increasing the contact time the media has to interact with the water.  

An easy way to rinse your media is to load it into the reactor, place the input pump into a five gallon bucket filled with RO/DI water, and the output tubing into another empty bucket.  Then just turn on your pump and give the media a five gallon flush.

If you are running carbon in your reactor, do NOT tumble it.  Activated carbon is basically just charcoal and will easily and quickly grind down into a fine dust and then be spread throughout your tank.  Rather, you need to use sponges on the top and bottom, and pack the carbon in tightly.

For GFO, you can gently tumble the media, so be sure to install an inexpensive ball valve immediately after the pump in order to regulate the flow.

I’d recommend this AquaMaxx Reactor below.  Be sure to pick up something like a Cobalt MJ1200 utility pump, a small ball valve, and flexible tubing in order to power the reactor and control the flow.

3) Kalkwasser Reactors

Kalkwasser is a German word meaning “lime water”.  I have absolutely no idea why we use the German term in this hobby, but we do, so deal with it!

When mixed with your tank water, Kalkwasser is a one-stop additive that is able to add both calcium and alkalinity into your tank at the same time.  For those of you who have been around the hobby for a while, you know that if you add two-part into your tank at the same time, you get this precipitate sludge which gunks everything up and does nothing to help your inverts.

Kalkwasser has another great side effect in that it raises the pH of your tank water.  Many hobbyists, especially in the winter, live in air tight homes with several people where the CO2 spikes, leading to a fall in pH.  When dosed slowly over a 24 hour period, kalkwasser can raise your pH.

I don’t recommend Kalkwasser reactors to beginners, because they are both over complicated and an unnecessary expense.  If you really want to dose kalkwasser, you can mix it into your ATO reservoir water, or set up a simple drip line to slowly dose it over the course of the day.

But, just in case you still want one, this Kalkwasser reactor from Two Little Fishes is inexpensive and does not require any additional pumps.  You merely plumb this unit in between your ATO pump and your tank, and the power of the ATO pump itself will both mix and dose the Kalkwasser to the tank.

A couple quick warnings about Kalkwasser

  • You never want to dose the white sludge that will settle in the bottom of the reactor.  It is way too high in pH.
  • Kalkwasser can take a toll on your pumps, gunking them up much quicker. So you will likely need to clean your pumps with a vinegar bath more frequently.

IV) Algae Scrubbers

Algae scrubbers are really a type of reactor that grows algae.  They basically all have similar designs.  They are some sort of dark box that is plumbed to pass tank water over a plastic sheet, and is blasted with lights encouraging algae growth. 

What is the media you may ask? The light!

The idea behind algae scrubbers is to out-compete nuisance algae in your tank by providing a perfect environment for algae growth inside the scrubber itself.  Then, as the algae grows inside the scrubber, it will consume phosphate from the water column, thus leaving less for nuisance algae to consume.

The only maintenance required is to occasionally remove the plastic sheet and scrape the algae off.  That’s it.

In this way, algae scrubbers function in a similar way to macroalgae in a refugium.

V) UV Sterilizers

UV sterilizers are probably some of the most misunderstood pieces of saltwater aquarium equipment out there.  Not only are they often misunderstood, but they are not utilized correctly.

Here is the gist: A UV sterilizer works by passing your tank water through a tube that contains a UV light (think black light). This light, while not killing pathogens, alters their DNA, thus inhibiting them from reproducing.

So, UV sterilizers can help reduce pathogens in the water column such as various bacteria, viruses, algae spores, etc, but it does not kill them and certainly doesn’t kill an disease that is present on your livestock.

But here is where people go wrong:

  • They think a UV sterilizer can cure fish disease… it cannot.
  • They don’t provide enough contact time between the pathogen and the UV light for it to be effective.  This is often because water is either pumped through the sterilizer too quickly, or the sterilizer simply isn’t large enough.

So what is a UV sterilizer good for? Tons of stuff.  It is a great preventative measure to reduce the number of pathogens in the water column, thus giving your livestock a greater chance for a healthy life.  Not only that, but UV sterilizers are known to produce crystal clear water and cut down on the amount of cyanobacteria and nuisance algae.

Don’t skimp on a skimmer, and no, it is not a replacement for a quarantine tank.

Aqua UV makes a high quality sterilizer, but it does come with a high quality price tag!

white pvc uv sterlizer on white background with blue end cap and label.

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