A Clearwater scrubber is an algae turf scrubber (ATS) designed to remove nitrates and phosphates from aquarium water by growing macro-algae on a mesh screen instead of inside the tank. The Clearwater ATS line, made by Santa Monica Filtration, works by flowing a thin sheet of water over a roughened screen under intense light, where algae colonize and rapidly consume nutrients. You harvest the algae every week or two, physically removing the nutrients from your system.

If you're dealing with persistent high nitrates or struggling to control nuisance algae in your display tank, a Clearwater scrubber is worth serious consideration. This article covers how these units work, which models exist, how they compare to traditional filtration methods, what realistic results look like, and how to set one up correctly.

How the Clearwater ATS System Works

Algae turf scrubbers aren't new. The concept has existed in the hobby since the 1980s, but the Clearwater line from Santa Monica Filtration brought reliable, purpose-built units to market for home aquarists.

The core principle is straightforward. Water from your sump or tank flows over a screen covered in rough mesh material. Under strong LED lighting tuned to the red and blue spectrums that algae grow best under, algae colonize the screen rapidly. Algae consume ammonia, nitrite, nitrate, and phosphate as they grow. When you harvest by scraping the algae off the screen every 7-14 days, you're physically removing those nutrients from the water column rather than just transforming them into something else.

What Makes Clearwater Different from DIY Scrubbers

DIY algae turf scrubbers are common in the hobby, usually made from plastic containers, rough screen material, and fluorescent bulbs. Clearwater scrubbers are factory-built with:

  • LEDs specifically tuned to optimal algae growth wavelengths (typically 660nm red + 450nm blue)
  • Slot-pipe flow systems that distribute water evenly across the screen
  • Acrylic construction with integrated lighting
  • Properly roughened screen surfaces that algae attach to better than smooth plastic

The main advantage isn't that DIY scrubbers don't work. They do. The advantage is consistency and convenience: a Clearwater unit is plug-and-play and designed to work right from the start.

Clearwater Scrubber Models and Sizing

Santa Monica Filtration offers the Clearwater line in several sizes, with model numbers that correspond to the screen area and tank volume they're rated for.

HOG Series (Hang-on Glass)

The HOG (Hang On Glass) models attach directly to the back of your tank or sump without requiring any plumbing. Water enters via a submersible pump included with the unit, flows over the screen, and drains back into the tank.

  • HOG 1: Rated for tanks up to 100 gallons. Roughly 4" x 4" screen area.
  • HOG 1.5: Rated for tanks up to 150 gallons.
  • HOG 2: Rated for tanks up to 200 gallons.

These are the most popular models because installation requires no drilling and minimal modification to your existing setup.

SURF Series (Sump-Based)

SURF models sit in the sump and require a small pump to pull water into the unit. They're slightly more capable than the equivalent HOG size because they can be positioned to maximize airflow and light penetration.

  • SURF 4: Rated for up to 200 gallons.
  • SURF 6: Rated for up to 400 gallons.

Sizing recommendation: if you're right at the boundary between two models, step up. A scrubber running at 60-70% of its rated capacity grows algae faster and removes more nutrients than one running at 100%.

Realistic Results: What You Can Actually Expect

After a break-in period of 3-6 weeks, a properly sized Clearwater scrubber should drop your nitrates noticeably. Most hobbyists report going from 20-40 ppm nitrate down to single digits, and in some cases zero measurable nitrate, within 2-3 months of consistent operation.

Phosphates drop more slowly, typically over 4-8 weeks, because phosphate is stored in rock and substrate and releases gradually. Don't expect your scrubber to drop phosphates from 0.5 ppm to zero in two weeks. It will get there, but the rock needs to leach its stored phosphate first.

Two things affect results more than any other factor:

  1. Harvest timing. Waiting too long means the algae starts to die off and release nutrients back into the water. Harvesting every 7-10 days is the sweet spot for most systems.
  2. Light intensity and photoperiod. The Clearwater LEDs run on a reverse cycle (lights on when your display lights are off) to buffer pH swings, and they need to run 18-24 hours per day for maximum growth.

Clearwater Scrubber vs. Other Nutrient Export Methods

ATS vs. Protein Skimmer

A protein skimmer removes organic compounds before they break down into nitrate and phosphate. An ATS removes the nutrients after they've already been processed. They're complementary, not competing. Most serious reef keepers run both.

ATS vs. Refugium with Chaeto

A chaeto refugium is functionally similar to an ATS: you grow macroalgae and harvest it to remove nutrients. The difference is growth rate. Under identical lighting, algae on an ATS screen grows significantly faster per square inch than chaeto in a refugium, because the thin water film over the screen gives the algae direct access to CO2 from the air. Chaeto submerged in water is CO2-limited. An ATS typically removes 3-5x more nutrients per watt of lighting than a chaeto refugium.

ATS vs. Biopellets or Carbon Dosing

Biopellets and carbon dosing (vodka, vinegar, two-part NoPox) work by fueling bacterial growth that consumes nitrate and phosphate, with the bacteria then skimmed off. They're effective but require consistent dosing and can crash if you overdose. A scrubber requires less precision: you just harvest regularly and it keeps working.

For more information on building out a complete filtration strategy, see our Best Aquarium Equipment guide.

Installation and Setup

For a HOG series unit, setup takes about 30 minutes:

  1. Attach the unit to the back wall of your sump or tank using the included suction cups or bracket
  2. Place the included submersible pump in the water
  3. Connect the pump to the inlet on the scrubber
  4. Plug in the LED light
  5. Confirm water is flowing evenly across the entire screen surface

The most common setup mistake is insufficient flow. If water isn't covering the entire screen in a thin sheet, algae will grow only in the wet zones and the dry areas will grow hair algae or nothing at all. Adjust the pump output until the whole screen is evenly wetted.

The screen comes pre-roughened, but some people add a light sanding with 60-80 grit sandpaper to improve initial algae attachment. It's not strictly necessary, but it can speed up the break-in period.

During the first two weeks, you may see brown or green slime rather than thick algae growth. That's normal. The community is establishing itself. Don't harvest during the first two weeks unless the screen looks truly overrun.

Our Top Aquarium Equipment roundup includes additional filtration options if you're still comparing approaches.

Maintenance and Long-Term Care

Weekly or bi-weekly harvest is the main task. Pull the screen out, scrape the algae into a bucket with an old credit card or plastic scraper, rinse the screen under tap water, and reinstall. The whole process takes under 10 minutes once you have a routine.

The LEDs have a lifespan of roughly 30,000-50,000 hours, meaning years of continuous operation before replacement. The pump is the most likely failure point and should be cleaned monthly by soaking in white vinegar to prevent mineral buildup.

FAQ

How long does it take for a Clearwater scrubber to work? You'll see some growth within the first week, but meaningful nutrient reduction typically takes 4-8 weeks. The algae community needs time to establish and grow thick enough to export significant nutrients. Nitrates often drop noticeably within 6 weeks; phosphates can take longer if your rock is leaching stored phosphate.

Can I run a Clearwater scrubber on a freshwater tank? Yes, ATS technology works in freshwater. Freshwater tanks generally have lower bioloads and are less common for ATS use, but the nutrient removal mechanism is the same. Some goldfish and cichlid keepers use scrubbers to manage the high nitrate production from messy fish.

Do I still need a protein skimmer if I have a scrubber? Most hobbyists run both. A skimmer removes dissolved organics before they break down, while the scrubber handles the resulting nitrate and phosphate. In very lightly stocked tanks, some people run only a scrubber successfully, but heavily stocked reefs generally benefit from both.

What do I do with the harvested algae? Compost it, put it in your garden as fertilizer, or throw it away. Some people feed it to herbivorous fish like tangs and rabbitfish, which works well if the algae is clean and free of pests. Don't put it down the drain in large amounts.

The Bottom Line

A Clearwater scrubber is a legitimate, effective nutrient export tool that earns its place in reef keeping and high-bioload freshwater systems. The HOG 1 handles tanks up to 100 gallons with minimal installation effort, and stepping up to the HOG 1.5 or HOG 2 gives you extra capacity for heavily stocked systems. Harvest every 7-10 days, keep the LEDs running on a reverse cycle, and give it 6-8 weeks to fully stabilize. The results are consistently good.