The Science Behind Gas Exchange (and Why Your Fish Need It)

We all know fish need water to survive. But what really keeps them alive is the oxygen in that water. Without enough of it, even the nicest reef tank can quickly become unsafe for your pets. Oxygen gets in and carbon dioxide gets out through something called gas exchange.

The good news is you don’t have to overthink it. Here’s why gas exchange matters for your tank and how a Salty Lid™ helps keep everything in balance.

What Is Gas Exchange, Anyway?

Gas exchange is just a fancy way of saying oxygen goes in and carbon dioxide comes out.

Fish breathe oxygen that’s dissolved in the water. They exhale carbon dioxide, which needs to escape into the air. Corals and bacteria also play a role, using and producing gases around the clock.

Without good gas exchange, oxygen levels drop, CO₂ builds up, and your pets get stressed fast.

Why Solid Lids Make It Worse

Glass lids or cheap acrylic covers can act like plastic wrap over your tank. Sure, they keep fish from jumping and water from splashing out—but they also trap humidity and slow gas exchange. That means less oxygen in the water and more headaches for you.

Symptoms of poor gas exchange can look like fish “gasping” at the surface, pH swings (often dropping too low), or sluggish, stressed corals. Not exactly the thriving reef you had in mind.

The Screened Lid Advantage

Here’s where a screened polycarbonate lid shines. The rigid polycarbonate frame gives you strength and a custom fit, while the fine screen material allows air to circulate freely across the water’s surface. That means your tank gets all the benefits of gas exchange without the risks of an open top.

So your fish get oxygen, CO₂ escapes, and your pets stay safe inside the tank where they belong.

Bonus: Evaporation Control

The other hidden win? While the screen lets air move, the polycarbonate frame itself helps reduce evaporation. That means you’re not constantly topping off with fresh water or dealing with salt creep on every surface nearby. More stability for your pets, less hassle for you.

Why Salty Lids™ Makes the Difference

There are a lot of DIY screen kits out there, but most leave gaps, don’t fit perfectly, or warp over time. That’s fine for “livestock,” but not for your pets.

Salty Lids™ are CNC-cut from UV-stable polycarbonate, designed to last for years without bending or yellowing. We precision-cut slots for lights, cables, and accessories so you get the airflow your tank needs without leaving dangerous escape routes. It’s the science of gas exchange, paired with craftsmanship that keeps your reef looking clean and professional.

Clear Waters Ahead

Good gas exchange isn’t just a science concept—it’s the heartbeat of your aquarium. Your fish, corals, and bacteria rely on it every single second. And the best part? You don’t need a PhD to get it right—you just need the right lid.

That’s why reef keepers everywhere are switching to Salty Lids™. Strong, clear, custom-fit, and built to give your pets the airflow and safety they deserve.

Because at the end of the day, they’re not just livestock. They’re your pets. And they deserve to breathe easy.