Cleaning the Water

There is quite a bit of equipment that goes into a saltwater aquarium. They broadly fall into 3 categories: Flow, filtration and lighting.

Flow

The ocean is constantly moving, and moving a lot at that. In the tank we simulate that by adding powerheads, which are, broadly, just things that push water. You can, and likely will, spend an enormous amount of time moving these around, perfecting the flow. The goal is to have more water movement at the top of the tank and at least some flow throughout the entire tank. Any quiet spots in the tank will attract debris and allow cyanobacteria (gross) to start growing. Plus, if there is too much flow near the sand, the sand will be blown throughout the tank and end up accumulating in all sorts of bad places. Usually on top of corals.

Corals, being somewhat immobile critters, require flow in order to have food blown past their polyps. Different corals have different flow requirements too, which is part of the reason that it’s important to have a range of different flow rates throughout the tank. Usually, the harder the coral, the higher the needed flow.

Filtration

There are a few classes of filtration: Biological, chemical and mechanical. All of them should be present in some capacity as they all serve different purposes. They can even all be present in a system with no external components! Though that is a much more niche thing that some people do.

Biological

Biological filtration generally refers to the bacteria that live in the sand and rock which break down waste. The purpose of the initial “cycling” period of a tank (letting it lie fallow for a couple months before stocking it) is to build up these colonies. There are bacteria which are responsible for converting ammonia, a toxic product of fish waste, to nitrate, also a toxic chemical. From there, a different bacteria will convert the nitrate to nitrite, which is significantly less toxic. This is referred to as the nitrogen cycle. There are also colonies responsible for dealing with other, less potent, waste problems. These guys can just do their thing without me getting in their business.

Chemical

Chemical filtration refers to things which directly remove chemicals and “dissolved organic compounds”, commonly referred to as DOCs, (dissolved food bits) from the water. This is how things like nitrites (produced via bacteria) are removed from the water. Without this you’ll end up with accumulation of nitrite to dangerous levels over time, as well as food for nuisance algae. Fortunately this is pretty easy to handle. Large soft corals (softies) are great at sucking nitrite out of the water as they use it for growth. Intentionally adding species of macroalgae, such as kelp, helps remove those DOCs too and hopefully out competes the nuisance algae.

This can also be handled via special filter media that is able to absorb specific things. Occasionally, when I need to remove something from the water, I’ll add a mesh bag full of activated carbon to an area that has high flow. This has come up when treating the tank for flukes, a parasite which infects fish. The medication is only supposed to be present in the water for a period of 48 hours (and redosed a few days later for a few weeks). This is the best way I know of to remove residual medication as well as the byproducts of the medication breaking down.

Mechanical

Mechanical filtration removes larger particles from the water. Things like sand which gets blown, larger chunks of fish waste, and leftover food get removed through this. A simple example of this is a filter sock which water passes through. This can be regularly cleaned and replaced so as to remove the organics before they get a chance to dissolve and increase ammonia load and DOCs.

The other example, which I didn’t understand while starting out, is the very rock in the tank. This will provide areas of dramatic flow reduction, allowing the floating particles to settle. Since these particles get trapped in the rock it will not resolve the issue of food breaking down but it’s still important! The cleanup crew appreciates it too. That’s the best place for them to hunt down fresh food, apart from just killing snails.

Others

There are also other methods of implementing these which are more complex. I’ll be going some of those when I talk about the sump.

Here’s a bonus Blenny as a reward for reading through all of this!