If you have not yet had the unfortunate experience of dealing with Red Slime in your aquarium, it will eventually happen. So whether you're dealing with it now or simply expanding your aquarium care arsenal, this guide to curing red slime is going to be just the ticket you need to keep your tank slime free for good. 

What Is Cyanobacteria?

Cyanobacteria (Red Slime) is a common pest that occurs in all aquariums and often plagues newer saltwater aquariums. It can show up anytime and takes on a slimy purple-deep red appearance in most cases but can also be black or green. It will blanket the sand bed, rocks, corals, and even equipment but thankfully it's pretty easy to remove because it lacks roots or any strong attachment to the surfaces it coats. 

Cyanobacteria is an aquatic photosynthetic bacteria and is technically not an alga, even though it is often referred to as "Red Slime Algae". It is not directly harmful or toxic but it is pretty ugly and can blanket your corals, blocking out light and causing them to starve.

The causes of cyanobacteria in your aquarium are not always directly obvious.  Nitrate and phosphate levels (nutrients) are often an area of interest in discussions about red slime but it will grow in both high and low nutrient situations.  It does seem to always start or grow the fastest in areas of minimal flow, typically on the sand bed. Over time, it spreads out onto the surrounding rocks and corals. 

How To Treat Cyanobacteria

  1. Increase water flow - Since red slime is not securely attached, increasing water flow will simply blow the bacteria into the water column where your mechanical filtration can remove it. 
  2. Manual removal - Use a turkey baster to blow the cyano off the rocks each and every day then siphon out large blankets of cyano as often as you possibly can. Running the siphoned water through a filter sock to trap the cyano is a great way to clean and siphon the aquarium without doing a water change. Together with increasing flow, manual removal takes time and it is important you clean out the cyano as often as you possibly can. After a few weeks, the cyano should subside and eventually stop coming back. 

Tips For Success

  • Use a 100-micron filter sock; this will clog quickly but be very effective at catching debris and cyanobacteria that get kicked up. You will want to change that sock daily to be effective at physically removing that cyanobacteria trapped in the sock. Bonus, your tank stays extra clean as well.
  • Dose the tank with beneficial bacteria like Microbacter 7 or similar bacteria supplements.  It is theorized that beneficial bacteria can help out-compete cyanobacteria in the aquarium and it has proven to be quite successful. 
  • If all else fails, use a chemical solution like Chemi-Clean to kill the cyanobacteria in your tank. Just keep in mind, the Cyanobacteria can grow right back after treatment so repeated physical removal is often required to get rid of it for good.