Macroalgae can soak up ammonia, phosphate, nitrate, heavy metals and even more!  As the macros grow, they take up all of these things, and then the moment we harvest (trim them), we are literally throwing away what is within them.  In a closed system, organics can get high so quickly.  Even with water changes and equipment to remove those organics, there just are not many ways to keep up with the levels that can accumulate in a closed system.  Especially if you’re talking about a seahorse tank!  Healthy seahorses eat 2-4 times a day, and create “waste” almost as quickly as they eat food!  Even in systems that do not contain fish that are considered “dirty”, there are processes constantly happening that raise the organic levels in a tank.  What typically happens is that nuisance algae grows in response to those high nutrients and organics, and you see the results as slimy algae on the glass and ugly hair or matting algae on the rocks or substrate.  No one wants that mess!  So, if algae will grow in response to high organics and light…..why not grow algae in a separate location (sump), and remove all of those things you can’t see when you trim the algae during a water change?

If you’d like to read more about the ways to use algae, click here!  However, I want to emphasize that keeping algae in an aquarium does not automatically remove nutrients and organics.  The HARVESTING or TRIMMING of the algae removes all of that bad stuff WITH the algae that you throw out or sell.  .

If you are reading about these methods AFTER you already have an algae problem within a display, there is still hope!  It takes a little bit longer, but you can still use algae in a sump refugium, scrubber or reactor to outcompete any nuisance algae in the display.  If you give the sump algae more light in the spectrum that grows it the fastest, it will take up nutrients so quickly, that the algae in the display will starve to death.


Obviously, taking up excess nutrients will improve water quality.  However, most forget that algae helps in other ways too!  During photosynthesis, the algae take up CO2 and give off oxygen that helps the fish.  During respiration (at night when the algae does not get any light), it takes up oxygen, and gives off co2.  Luckily, the amount of oxygen given off during photosynthesis is much greater than the oxygen taken up during respiration.  So, in a display tank, as long as slow growing algae is being used, the uptake and release are not making enough difference to affect anything.  However, when fast growing algae is used on a reverse light cycle (meaning the lighting on the algae in the sump turns on when the tank lights shut off), the algae is literally providing extra oxygen into the water at night.  Coral goes through the same processes as algae, so they are taking up oxygen at night themselves.  This is one reason ph drops at night.  When the algae is giving off oxygen at the same time as coral is taking it up, and vice versa, the ph remains stable and the tank is always oxygenated.


Algae is a great food for fish and pods.  In a seahorse tank, keeping algae in the display or sump will promote pod production.  Copepods (a great snack for seahorses) will multiply like crazy when there is algae to hide in and eat.  The copepods bring their own benefits to an aquarium (read more in my article interview with Chad Clayton of Reef Nutrition), and then the copepods become a food for the seahorses.  In a reef setting, the copepods provide that same balanced ecosystem, and the fish will also eat most of the algae in addition to snacking on pods.  Pods are also a huge benefit when a reef contains picky eaters like mandarin.