Hi saltwater aquarium fans,

Today I want to talk about a problem affecting a number of my Facebook friends and fans (thanks for the idea guys!).

This gunk means you have a problem...

This gunk means you have a problem…

If you have nasty slime growing in your saltwater aquarium rockwork or substrate which colouring ranges from black to blue, purple, red and even green; chances are you have a cyanobacteria outbreak…

Cyanobacteria is a photosynthetic lifeform placed by science somewhere between plants and bacteria. It thrives on nutrients primarily nitrates and phosphates but also uses silica from the water. It is a common pest algae in saltwater systems. People get confused about identifying it because of the different colours, but if it looks like slime it will almost certainly be cyanobacteria.

When saltwater aquariums are cycling pest algae can naturally grow then in a few days or a week disappear again as part of the changing life cycle in an ecosystem with changing nutrient levels. When your slime sticks around over a few weeks and is spreading; then you have problems.

You have two options; treat the symptoms (the algae itself) or treat the cause. Treating the symptoms will get rid of the algae but not stop it coming back, but if you are smart enough to discover and treat the cause then you have every chance of not seeing its ugly face ever again!

Causes of Slime algae:

1. Excess nutrients: this is the main reason you will see slime algae. Your system has too much dissolved organics in the form of nitrates (the end product of the nitrogen cycle) and phosphates (organic compound usually in the water from unfiltered water source/additives/food). These levels can gradually creep up in the water from many sources such as:

– overfeeding.

-dead/decaying marine life somewhere in the tank.

– using unfiltered tap water instead of RO/DI water.

– adding too much/poor quality additives to the water.

– unwanted phosphates in the water from additives/food/materials (eg some brands of activated carbon)

– too much bioload for the frequency/volume of water changes you are currently doing.

Its important to remember that if you have a large outbreak you can get a negative reading for nitrates because the algae is using the nitrates as quick as they are being produced!

2. Inappropriate lighting: cyanobacteria thrives on light in the red spectrum and can sometimes appear when bulbs are aging (causing the light spectrum to change) or there is too much light or sunlight hitting the tank.

3. Too much heat: sometimes part of the cause of pest algae especially slime algae is excess heat, if the tank is consistently over 80’F or if the temperature fluctuates a lot slime algae can thrive.

4. Low water movement: slime algae LOVES it when water movement is low and will mostly thrive in “dead spots” of very low water movement in the tank. The total volume of your tank should be turned over at least 10 times per hour.

The main reason for your slime algae is most probably excess nutrients but lighting, excessive heat and too little water movement may play a contributing role.

Getting rid of the algae itself is pretty easy and should be done (preferably after you find out where the cause lies) by syphoning and sucking out the algae from the substrate or rock using a python or hose replacing the algae water with brand new pristine stuff you have made up beforehand.

The cause of your pest algae outbreak is likely to be too much nutrients, where are these coming from? You need to systematically go through every thing that goes into your water from the water source itself to food, additives, phosphate containing filter media, partially clogged skimmer/pumps/powerheads, not doing enough water changes,the expired filter on your RO unit…the list goes on and every marine aquarium owner will have a different list to go through. These nutrients are coming from somewhere and to cure your problem for good you need to rule them all out one by one using some good old detective work. As every potential cause is tested you need to either test the water for nutrient levels or wait to see if your algae goes away and stays away to find the underlying cause!

Curing your red slime outbreak:

A clean protein skimmer can help you

A clean protein skimmer can help you

After you have figured out the causes for your red slime you can quickly get rid of the existing stuff by:

1. Doing more regular partial water changes and changing bigger volumes (like 10 or 15% at a time every few days).

2. Adding a protein skimmer to help get rid of the dissolved organic waste.

3. Get an RO unit instead of using nasty tap water.

4. Introduce some macro-algae species to your tank to outcompete the red slime for nutrients.

5. Feed less food (you should only feed what your pets can eat in one or two minutes).

6. Add more live rock or live sand; naturally reducing dissolved organics.

7. If you detect excess phosphates in your water read the labels of everything you add to the tank and replace products/media/additives containing phosphates or add a product such as Phosban or use a phosphate reactor.

8. Clean your substrate more thoroughly getting out all the settled detritus.

9. Increase water movement; you can never have too much multi-directional water movement!

10. Change your bulbs if they need replacing; every manufacturer will have a recommendation for this.

11. Employ the help of a secondary heater or chiller to keep the water temperature more stable or lower it.

So, there is a whole lot of things you can do to wipe out your slimy enemy; but you really need to find out the cause of your algae outbreak (even though it can be annoying!) to stop it from ever coming back. Sure it takes a bit more work, but if you make the effort to do this you have beaten the slime!

Saltwater Aquarium Advice