Reef It Simple, Part 2: Let's Talk Filtration
This is part two in a series about how you can take the complexity out of keeping a saltwater reef tank. Make sure to catch part one, covering aquarium chemistry, to get up to speed.
Now that you're familiar with all of the different numbers for a reef tank and how they work, it's time to talk about filters. As we talked about before, filtration in the marine and reef environments is considerably different from what you'll find in freshwater. But just because it's different doesn't actually mean it has to be more difficult. There’s a lot to talk about here, but the concepts are really very easy. So without further ado, let’s dive in.
What you need to know first off is that water in the tank gets dirty. There’s leftover food, waste from the fish, waste from the corals…and it’s all just there floating in the water. We need a way to get that stuff out. We do that by filtration.
- Mechanical - Removes stuff from the water
- Biological - Breaks down stuff in the water
- Chemical - Treats stuff that's in the water
The bulk of your filtration in a reef system will happen as water passes through the rock and sand that you have used to set up your aquascape (don't worry, aquascape is just a fancy word that we use for "placing your rock and sand"). In a freshwater system, the good bacteria will live in your gravel, but it primarily lives inside of a filter that you've added to the setup. Because reef tanks require significantly more stringent filtration, it's important that you're using the right kind of rock and sand, as well as making sure that you have enough water movement.
First thing's first: we have to get water moving through your rock to start establishing your biological filtration via the nitrogen cycle. As a general rule, how much water movement you need in your tank will depend on the types of corals that you want to have. Soft corals, for instance, have somewhat lower requirements. But if you want a tank that is primarily dominated by SPS (small polyp, stony corals, like acropora pictured below) you will need to have some pretty serious water moving around in the tank.
- Soft Coral: 10-15x display tank volume per hour
- LPS Coral: 15-20x display tank volume per hour
- SPS Coral: 30x+ display tank volume per hour
Now you'll notice that I said "guide" as opposed to "rule". That's because you'll find people who are using only 15x turnover but they have absolutely stunning SPS corals. There are very few hard and fast rules in reef keeping and water flow definitely has a lot of flexibility.
Sumps provide a number of benefits, but not the least of which being a larger overall volume of water in the system. If you think back to the previous post, you’ll remember that stability is key in a reef system. The more water you have, the more tolerant the system will be of changes. Think of it as a real-life “drop in the bucket” scenario.
Filtration in the reef tank can seem really complex, but it’s actually quite simple. It’s easy to get overwhelmed by the options and decisions, but keeping the basics in mind is what will help you to make an informed choice. In a freshwater tank, we let the filter cycle and then we decorate to our heart’s content. Only live plants really serve the purpose of both decoration and filtration. But in the reef, almost every part of the tank plays a part in the filtration dance.
You can make filtration in the reef tank as complex as you want, but often times adding in new pieces before you’re aware of how they work (and the effects that they’ll have) can cause the new hobbyist heartache. We’ll dive in deep with skimmers, media reactors and all kinds of other filtration devices in another post, but for now you have the basics that you need to know about filtering your reef tank.