Cyanobacteria | Red Slime Algae And How You Can Get Rid Of It

Cyanobacteria or red slime algae is actually a strain of photosynthetic marine bacteria. Sometimes referred to as blue-green algae (BGA), cyanobacteria thrive in nutrient-rich water, sufficient lighting, and where water flow is nearly stagnant.

Red Slime Algae | Is It That Big Of A Deal?

So why is red slime algae so disliked, and sometimes even dreaded?

red slime algae on sandbed

Red slime algae on a sandbed

In moderate amounts, they form unsightly patches of dark red on the sandbed and on live rock. Not a big deal, as it can be easily siphoned out with every water change. The annoying thing is that they will just show up again after a few days in exactly the same spots.

When they reach plague proportions — and we are talking about really neglected tanks here — red slime algae smothers everything in sight. Sandbed, rocks and even corals, are not spared.

But again, even in the most dire of red slime algae infestations, a thorough siphoning does the trick. It does not fix the problem, as we will discuss later, but at least it lets the tank look its best again.

Is That Red Slime Algae On My New Live Rock?

It is important not to confuse red slime algae for the desirable and beautiful red or maroon encrusting algae that sometimes comes on live rock.

One of the earliest beginner’s mistakes I made was throwing out a perfectly good piece of live rock, out of a batch I had just purchased, because I thought that it was covered in red slime algae. Just remember, if the red stuff comes off easily when you touch it or blow water over it, it is red slime algae. If it looks like red velvet and holds fast to the rock, it is good!

What Can You Do To Rid Your Tank Of Cyanobacteria?

Avoid Overfeeding

Cyanobacteria thrive in nutrient-rich water. Overfeeding the fish also feeds red slime algae and encourages it to profilerate.

When feeding frozen foods, be sure to thaw and throw away the nutrient-laded juice before adding it to the tank. I would also avoid flake food entirely as it pollutes the water more than pellet foods.

When feeding corals, be sure to turn off aquarium pumps and target feed only as much as required. Broadcast feeding of coral foods should be avoided if you have a red slime algae problem. Corals need only be fed once or twice a week.

Increase Water Circulation In The Tank

As mentioned, red slime algae thrives in areas of poor flow. Increasing circulation in the tank by adding a couple more powerheads, or better yet adding powerheads that are programmable so that they pulse and pump water at different velocities throughout the day.

A neat little trick I learned from one of my local LFS owners was to group two or more smaller powerheads together, setting each cluster at opposite side of the tank. Each powerhead runs on its own timer and comes on at different times during the day — sometimes two at a time, just one, or all at the same time. The powerheads in each cluster can also be angled differently, creating different directions of flow depending on which is on. Talk about random turbulence!

By no means a cure in itself, brisk water movement in an aquarium minimizes dead spots which is where red slime algae loves to settle.

Do More Water Changes

Ok, so slacking off on water changes has led to high nutrients in our tank, which in turn has led to to a cyanobacteria bloom (and probably high nitrates as well).

Stepping up water changes and keeping to a consistent weekly schedule will help to restore our water to more pristine levels.

Fighting red slime algae is a lot like battling high nitrates or a diatomaceous algae bloom. It requires only time, patience and lots of water changes!

Change Out Old Aquarium Bulbs

If your are using metal halides, power compact, T5 or VHO fluorescent lighting it is necessary to change out your bulbs every 9 months.

Older bulbs will drift as far as their PAR values and can lead not only to a cyanobacteria bloom but also an increase in nuisance algae.

Siphon, Siphon, Siphon!

This one is pretty obvious. And there’s nothing more satisfying than watching sheets of red slime algae being sucked into a clear tube and into a bucket.

red slime algae aquarium wall

Red slime algae on aquarium wall

My favorite for siphoning detritus and mulm out of my tank is 1/2″ diameter clear rubber tubing. The one I’ve used for years is about 7 feet long, more than enough length to reach the sandbed in the tank. I’ve tried using vinyl airline tubing, but I find it tends to kink easily which blocks flow. And because vinyl is lighter than rubber, the other end sometimes doesn’t want to stay in the bucket, getting saltwater and detritus all over my ceramic-tiled floors. I find 1/4″ tubing to be unsuitable as well because it gets obstructed easily with larger grains of sand.

It is very important that cyanobacteria be siphoned off carefully and meticulously, with all pumps and powerheads turned off. We do not want any stray bits of cyano floating to other areas of the tank where it will settle and spread.

And for the same reason, never attempt to blow red slime algae off of rock with a powerhead or turkey baster!

Reef Cleanup Crew To Battle Red Slime Algae

In my experience, only the small orange-legged hermit crab will eat red slime algae.

hermit crab eating red slime algae

Orange-legged hermit crab eating red slime algae

These tiny hermits, with their characteristic shells that measure an inch across, are beautiful creatures that are getting harder to find. You would be better off taking the abovementioned preventive measures to clear up red slime algae rather than relying on any one species to do it for you.

Red Slime Algae And LED Aquarium Lighting

Many aquarists have reported this phenomena. When they switched over to their brand-new LED lights they suddenly noticed a bloom in cyanobacteria.

And I have witnessed this myself on one of my own tanks when I switched over from T5 lighting to the more eco-friendly LED lighting. Cyanobacteria-free for many years, I started noticing small clumps of red slime algae appearing on my sandbed after a few days under the new lights.

If you think about it, it makes sense. We are, after all, dealing with a light-loving species of bacteria here. And when hit by the glorious, deep-penetrating PAR of LED lights, red slime algae really starts to show its true form.

Should You Use Chemicals To Control Cyanobacteria?

There are several commercially available products that claim to be able to remove red slime algae. Most of these are antibiotics, usually erythromycin, and they do work to some extent depending on the severity of the red slime algae problem.

Unfortunately, like all antibiotics, red slime algae medications will also kill off the good bacteria in our aquarium systems as well, possibly throwing everything out of whack, leading to ammonia or nitrite spikes. And as we know by now, ammonia and nitrite spikes can wipe out most, if not all, of your livestock.

Maybe I am over-dramatizing it a bit, but I feel it’s always better to be extra cautious when it comes to adding chemicals, and medications in particular, to our tanks. Nothing beats good, old fashioned dilligence when it comes to battling red slime algae.

Read more about:

Saltwater Aquarium Maintenance

Algae Control

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