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If there is one question I got the most while working in any aquarium store, it was “what the heck is cycling a tank?”. For something so fundamental to starting an aquarium it was so sad to hear how many people had been misinformed on it. Luckily, talking it to plenty of families who ended up with a goldfish got me pretty good at explaining it.

So, the question still stands; What is cycling?

When you hear someone talking about “cycling” their tank they are talking about letting their tank run its course through the nitrogen cycle for the first time. Nitrogen enters your tank through food, fish waste, or sometimes special tank additives. That nitrogen quickly grabs whatever hydrogens it can and forms ammonia (NH3). Ammonia can be toxic to fish and become lethal once concentrated enough. This is what you commonly hear described as “new tank syndrome”. Luckily, some friendly kinds of bacteria (Nitrosomas) will oxidize this ammonia, now turning it into nitrites (NO2-). Unfortunately, nitrites are still toxic, so we need another friendly bacterium (Nitrobacter) to add another oxygen to our nitrites. This results in nitrate (NO3-), which is much less toxic than its two cousins, ammonia and nitrite.

So, in short:

• Ammonia is formed after nitrogen is introduced to the tank through various means

• Nitrosomas oxidize the ammonia, forming nitrites

• Nitrobacter convert those nitrites into nitrates

Now, this process typically takes about a week to two weeks to run its course. However, many things can affect the chemistry in the tank and thus effect the cycle. I have seen a tank cycle in as little as three days, and I have seen some take a little over a month to finally finish. It is often recommended you use a product that supplements these various species of bacteria into your aquarium. More often than not, the bacteria do not naturally reproduce enough to quickly combat toxins.

Alkalinity is the measure of the ability to resist changes in pH, or the total acid bonding ions present in a solution. It is measured in milliequivelents per liter (meq/L). Most often you will see alkalinity expressed as carbonate hardness (dKH). While both participate in acid neutralization, carbonate hardness is only the measurement of the carbonate type of ion (CO2−). Acid bonding ions can be plenty of other species, but the carbonate ion is typically the most common in water. Another way of putting it is alkalinity is not just KH but KH is alkalinity.

In my experience, pH and alkalinity play hand in hand. KH prevents acids from showing up and causing your pH to swing. If the alkalinity of a tank is too low and you keep adding pH buffer, the pH will keep getting pulled back down. So in order to have a consistent pH, it is best to have a consistent alkalinity too. I prefer using products that buffer the pH and alkalinity at the same time, though you can use 2 different products to get the numbers just right. But try doing a water change first to see if that fixes the problem before adding any buffers. Many water supplies have a high KH, so performing a water change might be enough to buff your KH back up. There are also tricks like using crushed coral, aragonite, or sodium carbonate (soda ash) to raise your KH.

The term pH stands for "power of Hydrogen" and is a measure of the number of hydronium ions (H3O) in your water. Low pH corresponds to high concentrations of hydronium (acidic), whereas high pH corresponds to low concentrations of hydronium (basic). Pure H2O has a pH of 7.0, which is completely neutral. But not all of the water within the said solution will stay water! Two water molecules can actually bump into one another and steal hydrogens. This results in our friend hydronium (H3O) and their cousin Hydroxyl (OH-). This sort of dissociation and recombination takes place constantly in our tanks.

Buffers are often seen at stores as a way to control your pH. These buffers are chemical mixtures of a weak acid and its conjugate base. The mixture of these two either increase or decrease the number of hydronium ions in the water, raising or lowering the pH. Most freshwater fish do best at a pH of 6.8 to 7.6, although certain fish may require higher or lower levels (some examples being various species of cichlids, which thrive at pH as high as 9.0).

Water conditioners, or dechlorinators, are a common tool in aquarium keeping and cleaning. Chlorine exists in water as dissolved chlorine gas (Cl2) and is used to kill bacteria in our water supply. However, it evaporates very quickly, so some municipalities use the more stable chloramine (NH2Cl). Water conditioners are reducing agents (these include Sodium hydroxymethylsulfinate and Sodium hydrosulfite), able to transfer electrons and oxidize themselves in the process. This results in chlorine splitting into two separate, non-toxic chloride molecules (Cl-). The same process breaks the bonds between chlorine and nitrogen in chloramine. Unfortunately, this results in the nitrogen splitting off and forming ammonia (NH3). Some dechlorinators plan for this by having a binder that forms an iminium salt with the ammonia, making it non-toxic.

Phew! A lot of chemistry!

So, let us sum it up in a couple of bullet-points:

• Reduces chlorine to harmless chloride

• Breaks the chloramine bonds, creating chloride and ammonia (which is neutralized via a binder or the nitrogen cycle)

Filtration is a big part of setting up and keeping an aquarium. There are many types that you may come across while searching for the perfect fit for your tank and life, but 3 main types usually come to mind: Hang-on-back filters, canister filters, and sumps. All have their pros and cons but have the same sort of idea. Ideally, you want to have 3 stages within whichever filter you choose for your tank. You will want mechanical filtration (in the form of sponges or filter floss), chemical filtration (most commonly carbon, but can be a multitude of different products), and biological filtration (the beneficial bacteria we mentioned in our “cycling” post).

First, lets start with the easiest to understand and setup; the hang-on-the-back filter. These filters simply hang on the rim of your tank and suck water through a long intake pipe that sits in the water. The water is then sent through whatever type of filtration is placed inside, then pours out of the filter and back into the tank like a waterfall.

Pros:

These filters are very easy to setup and clean. Most hang-on-back filters simply have a lid you remove and then you can pull out everything inside. They are also very customizable, even if it is built for a company’s specific type of cartridges.

Many of these filters also have adjustable flow, controlled by a sliding switch or a wheel on the front or side. This makes it so you can slow down the water for slower fish like bettas or crank it up for as much filtration as possible.

Cons:

Hang-on-back filters are not exactly discreet. They are clunky and often require more space to fit. This means you may not be able to push your tank flush against the wall and its profile view may be a little less than slim.

These filters also require you prime them by pouring water into it every time you start it back up. If you do not, you stand the risk of burning out the motor of the pump.

Some people also just do not like the sound the little waterfall makes.

Now, onto the next contender, the canister filter.

A canister filter is basically a sealed bucket with an intake and output hose that both sit inside the tank. The canister itself sits under the tank. Inside the canister are several trays or slots where the water runs through multiple types of filtration, and then is pumped back up into the tank.

Pros:

A canister filter takes up very little room and is very customizable. It is one of the most quiet options on the market while also being a very powerful filter.

Cons:

Unlike the hang-on-back, it can be tedious lugging the canister out from under the tank and taking it apart to clean all of its bells and whistles. This also leads to some higher chances of spills (I recommend cleaning them in a bathtub or shower so that if you do spill anything, its already taken care of).

Canister filters can also be a little pricey. They often come with a lot of extras that you may or may not want for your aquarium.

Finally, the sump. The biggest and most complex out of these three filters. Sumps are essentially another tank that sit below your display. They have different chambers for different filter media. Water comes into the sump through an overflow (this is typically plumbed right into the tank or is added with an overflow box which, IMO, looks just like a hang-on-back). At the other end of the sump a return pump (typically sold separately) shoots the water back into the tank.

Pros:

EXTREMELY customizable. Sumps can be customized for just about every type of tank you can think of. They can also be connected to multiple tanks to simplify cleaning.

When using a sump, you are increasing the total water volume of your system. More water volume means more wiggle room. For example, if you add an extra drop of pH buffer to your 55 gallon, it won’t be a big deal. But if you add an extra drop to your 5 gallon you might have a problem.

Cons:

These take up a lot of room and can be extremely expensive to set up. It is essentially a separate tank made out of acrylic with all kinds of plumbing connecting it to your display.

The more complex plumbing can also result in a mess if not handled correctly.