Equipment. The protein skimmer

In a system where we "push" hard with feeding (mine, our "feeding mash"), the risk is not "dirtying" the water but… build-up.

In nature the reef recycles everything almost perfectly. In the aquarium it does not: in the aquarium we are the refuse collectors.

Let's look together at the various export systems. As always we will cover a bit of everything, from skimming to the refugium. We will give each one its own article, otherwise it gets too long. I would say let's start with the piece of kit everybody uses 😉

The skimmer (protein skimmer)

Many reefkeepers, including my former self, see the skimmer as a simple "dirt filter".

In reality it is a physico-chemical reactor that exploits something very elegant: the polarity of molecules.

Organic substances (proteins, lipids, food residues, mucus) are often amphiphilic: they have one part that loves water and one that avoids it.

Before understanding how to tune it, let's get to know it…

The physics of the bubble: surfactants and polarity

The skimmer exploits the nature of organic molecules (proteins, fats, excess amino acids). These molecules have a hydrophilic head (water-loving) and a hydrophobic tail (water-hating). The hydrophobic tail sticks to the air bubble; the bubble rises and carries the molecule up to the cup. The longer the bubble stays in contact with the water, the more molecules it "loads" onto itself. It works thanks to surface tension.

A million microscopic bubbles are infinitely more effective than a thousand large ones. The total exchange surface is the key.

1. 1Head: loves water the hydrophilic part stays facing the water
2. 2Tail: hates water the hydrophobic part clings to the bubble
3. 3The bubble rises and carries the molecule up to the cup
4. 4Many small bubbles far more surface to catch the dirt

Many small bubbles = far more surface to catch the dirt.

How a bubble carries dirt away.

The chemistry of removal: what are we taking out?

• Proteins and organic compounds, before they become ammonia.
• Mucus produced by corals and bacteria after feeding.
• Dissolved organic compounds, which would otherwise yellow the water.

Not everything is intercepted, but a significant part is. And it is removed before it enters the nitrogen cycle.

Tuning: the foam's breaking point

This is how I see it: there is no universal setting, there is the one that suits the moment and that tank. There is no such thing as "skimming to remove a full cup every X days"… It is a balance, not a race to fill the cup.

Dry skimming (thick, dark foam): useful when we want to keep a little nutrient around and not strip the system too much.

Wet skimming (light foam, like weak tea): essential when we are feeding heavily or when the system is loaded. It helps remove mucus quickly, along with part of the organic compounds released, even during chemical warfare between corals.

1. 1Dry thick, dark foam: removes less, leaves some nutrients
2. 2Wet light, tea-like foam: when you feed a lot or the tank is loaded
3. 3Dirty neck: −70% the skimmer loses up to 50-70% of its power. The neck matters more than the cup.
4. 4Tip skimmer air filtered through soda lime (CO₂ scrubber): pH rises by as much as 0.2-0.3

The neck matters more than the cup.

Sources: [1]

Dry or wet skimming, and why a clean neck matters.

Maintenance: the detail that changes everything

The skimmer neck is where separation happens. Within a few hours a bacterial biofilm forms on the neck that bursts the bubbles before they reach the cup.

A skimmer with a dirty neck loses up to 50-70% of its removal capacity. If we do not keep the neck nice and clean, we are fighting like gladiators in the arena, but with a blunt sword.

It is not so much about cleaning the cup, but about keeping the inner neck clean, where the skimming happens. Personally I clean it twice a day (helped by having a wiper under the lid that sits against the inner neck: I just turn it ten times or so), and every 2 days I clean the wiper.

Skimmer inhibition

It has happened to all of us: we put our hands in the tank or feed, and the skimmer "goes mad" and the bubbles disappear.

Why does it happen? The fats on our skin or the oils in some foods break the surface tension: the bubble can no longer hold on to the organic molecule.

When food is dosed the skimmer may go mad (too much foam) or collapse (no foam). It needs watching: the more attention we give it, the better it works.

Technical tip

The skimmer draws in litres of air every minute. If the room air is loaded with CO₂ (people at home, windows closed), the skimmer will push CO₂ into the water and can lower the pH. And, as we saw in the previous articles, we do not like low pH.

The clever move: connect the air line to a soda lime filter (CO₂ scrubber). It is not compulsory: it is one more tool. We will see pH rise by as much as 0.2-0.3 points, and a high pH (8.3-8.4) speeds up Acropora calcification incredibly.

So…

When we tune our skimmer we do it taking into account the variables our system (the tank) is giving us, and not because a protocol tells us it must be tuned that way. Every tank has its own balance and it is up to us to find it, experimenting and having fun.

Happy reefing, everyone!

Who wrote this article

Sources

1. National Center for Biotechnology Information, PubChem (2026). Soda lime (CID 66545795), GHS Classification. U.S. National Library of Medicine.