How to rid your tank of Red-Slime!


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It seems like there are a lot of people lately who are battling red slime algae in their tanks, some have seemed to be doing so for a long time with no avail. Well, I have beaten this problem, it was simple, quick, and with out ANY additives . . . chemical or organic. I figured that maybe I could share some light on the subject as to how I beat it, and prevented it from retuning. I did this over six months ago, and have never seen it since. I had an outbreak that was so bad, you could not tell there was sand on the bottom of my tank. No joke! It was red, thick, stringy, and waving in the current as if to say "f@#K you, I am still here!"
For starters, red slime is actually not a form of algae at all, but rather a strain of bacteria which has evolved over the ages into its present form. The following is taken from an informative website,
"Red slime algae is actually not a "true" algae at all, but classified as a cyanobacteria. Often considered to be the evolutionary link between bacteria and algae, cyanobacteria are one of the oldest forms of life on earth and date back at least 3.5 billion years. These organisms produce oxygen as a byproduct of photosynthesis, and scientists believe that if it weren't for this microscopic organism, there would be no blue skies on Earth.
Commonly referred to as "red slime" algae, the name cyanobacteria literally means "blue-green" algae. Despite the naming, only about half of these organisms are actually blue-green in color. Most forms found in saltwater are other colors, ranging from blackish green to blue-green, from orange-yellow to reddish-brown, and often appear deep purple to fully black in color. Starting out as small patches, it spreads out from there as a mat of sheeting covering."
Although red slime is not actually an algae, it has very similar properties as algae does. The driving forces that cause it to grow are very similar that that of the typical algaes seen in reef tanks. Improper lighting, excess nutrients, carbon dioxide accumulation are all contributors to the growth of cyano.
Having lighting that is in the wrong spectrum is one thing that may very well lead to an outbreak of any algae, but especially red slime. I think that most of us are using the correct lighting sources for aquariums, but that does not mean that this is not your cause. Old bulbs can shift spectrums as they age, which will create an ideal growth environment for any algae. Try changing your bulbs. Dont change them all at once so that you dont shock the animals in your tank, but rather one at a time every week or so. Changin your bulbs is probably the easiest thing that can be done, and in many cases is the source of the problem.
Another problem may be that the light source is on for too long a period. True that over a natural reef, there may be light 12 out of the 24 hours in a day, but if you really think about it, the intensity of this light is only at its maximum for about 2-3 hours a day, and sufficient light for about 8-9 hours a day. If you turn on your lights for 12 hours a day, at full strength, then you are providing far too long of a lighting period. Try limiting the amount of time that lights are on to 7-8 hours a day. A good starting point is to cut the amount of time that your lights are currently on for in half. Then slowly bring the time period up over the next few weeks. Keep adding a half an hour every couple days until you reach 7-8 hours. If you see the cyano return, then back it off a little.
Adjusting the lighting is the easiset method to dealing with a cyano outbreak, but it is not always the solution. If either of these dont work, then keep reading.
Another fuel for the growth of cyano is an excess of nutrients. This is the most commonly thought of source for an algae bloom, but is not always the case. Excess nutrients can come from only two places. And you are adding both of them. They dont just appear out of nowhere. Phosphates, and nitrates are the two most common nutirents found to promote algae growth. These can come form a poor quality water source and excess feeding.
For startes, RO water is a must. RO/DI is even better. Using either of these as your water source will GREATLY aid in your battle. Expecially if you are currently using tap or another form of unfiltered water. Using RO or RO/DI water will eliminate any excess nutrients that may have been present in your source water which will help to reduce the accumulation of any excess nutrients.
Another cause for excess nutrients is over feeding. Feeding any aquarium properly is a difficult task for anyone, but especially beginners. Most of the time, people over feed their tank, BIG TIME! Rarely do people under feed a tank, otherwise their fish would be dead. This is the only area that I cannot give advise on as I dont know what kind of fish you guys keep, or what kind of food you are giving. But as a general rule of thumb, feed only enough food that it is all gone in under five minutes. I do advocate feeding on a daily basis, but some systems just cannot handle this. Personally, I feed about every other day. I may go two days once in a great while, but I found that feeding every day was too much for my system, and I got Cyano. Most people would be surprised to know that fish could go a good 4-5 days without food and be perfectly fine. I dont suggest this, as it is just mean to starve you fish, but I tell you as a frame of reference. So as another defense, cut down on feedings. Maybe less food, or less often, or both.
Another probelm that causes a buildup of nutirents is an insufficient cleanup crew. The buildup of detritus, uneaten food, etc, all breaks down and ends up as nitrates. Food for the cyano. Try bulking up the janitors if this is a problem in your tank. And if you are looking for something that eats red slime, dont hold your breath. I have tried every single animal that is claimed to eat red slime, and none of them did, so stick with the usuals to keep detritus and decaying matter to a minimum.
Keeping filtration equipment clean and functioning properly can also aid in the reduction of nitrate and nutrient build ups. Clean powerheads, pumps, any sponges, filter media such as bio balls, etc. AND KEEP YOUR SKIMMER CLEAN! If you only clean one piece of equipment in your tank, make it you skimmer. This is one of the best lines of defense the aquariust has against red slime. Empty your skimmer cup regularly like its your job.
Another problem that can fuel the growth of red slime is an accumulation of carbon dioxide. Cyano is similar to algae in the sense that it uses CO2 as a food source. CO2 can build up in a reef tank if their is too little flow. This is a very simple problem to fix, it often means simply the redirection or replacement of a powerhead. Check to see that you are getting good flow in your tank and that there are no dead spots. At a minimum, 10x turnover per hour is needed, with 15x-20x being even better.
This next step IMO, was the most beneficial in the removal of red slime as well as general well being of the tank. I used to do one 10% water change once a month. I then switched to doing 5% on a weekly basis. The difference in water quality was remarkable. My tank looked clearer, cyano went away as did the hair. Levels stabilized, and fish activity and coral growth improved. Try doing some smaller water changes more frequently. I PROMISE IT WILL HELP! It may not make your cyano go away as it may be caused by somthing else, but the general well being of your tank will improve.
Also, manual removal of cyano with a turkey baster is often very necessary to aid in its disappearence. This is much easier to do after the lights go out, because there is less of it when the lights are off for a while.
I have said this before, and got som flak for it, but I stand by it. The use of any chemical products is not recommended, nor are they reef safe. the products used are an antibacterial agent. Granted it does kill the cyanobacteria, but it takes out teh good bacteria along with it. Although many people have used these products, and have had good results of eliminating the red slime, it is a temporary fix for an underlying problem. Fix the source, and it will go away on its own. A chemical additive is NOT a good thing to use, it will take out the good along with the bad and may cause a mini if not full recycle of the tank depending on the doasage.
In summation, there are some key steps to the elimination of red-slime:
1. Adjust lighting. Change bulbs, or photoperiod.
2. Keep feeding to a minimum. Try reducing the amount or the frequency of feeding.
3. Keep equipment running properly and clean.
4. Increse flow rates.
5. Increase water change frequencies.
I would not suggest doing all of these all at once as it could be a lot of work, and a big change. Rather, try changing one at a time in a sort of guess and check pattern.
I started with reducing the feeding. Then I reduced the photoperiod (didnt change the bulbs thought as they were only a month old). I then shifted the direction of the powerheads. All this I did in one day as it was all simple stuff. At this point I began manual removal of the cyano with a turkey baster. Then, I cleaned all of the equipment in my tank, and did a water change.
The next morning, the red slime was gone. I continued with doing weekly 5% water changes, and regular cleaning of my skimmer cup. It has been over six months since i have seen any hint of cyano, and I have never seen it since.
I know that some, if not all of this has been stated at one point or another, but these are my experiences, clear and concise. I hope that this helps some of you out. I know that it can be frustrating, but I am speaking from experience here when I say that it can be gotten rid of PERMANANTLY!
Let me know if you have any questions.


Active Member
P.S. I just found out that there is a 10,000 character limit. That post is EXACTLY 10,000 characters long!:D
Example of Red-Sliime [a.k.a cyanobacteria]


thanks for the info! as a first timer with red slime algae, that helps me tremendously!! thanks again!!:D


Do I smell a sticky? Great post...this stuff in my refuge where lights are on 24/7. I know some find this a positive, as it is a good food source for pods, but i worry it is the cause of my macro disappearing. Could this be the case?


Nice job Justin, probally sticky worthy! ;)
On the subject. A lfs, tropicorium for anyone near the area, has said they actually encourage this growth in the tanks they use for breeding fish. Anyone ever hear of something like that? Does it encourage breeding or something else?
Thanks Justin!
I started using RO Water and changing water more frequently. Just as you said, I got less Red Slime over time. I am now fighting a winning battle. :D


Active Member
Interesting thread. Worth investigating more. I would like to see this made into a sticky as well, especially once we find out more about this method. Thanks for the input Justin. Good stuff! :cool:


Active Member
Wow . . . this came back from the grave now didn't it. I didn't think that anyone read it!
Well, glad it helped.


Active Member

Originally posted by JustinX
Wow . . . this came back from the grave now didn't it. I didn't think that anyone read it!
Well, glad it helped.

Hell I have it printed out @ home!


Active Member
Nice job!
I had small patches under all my rocks. I couldn't get water to flow under all of them no matter how many PH I used.
All I did was to add a closed loop 700 GPH PH to the bottom back of the tank going corner to corner with a PVC pipe pushing out and up. Never came back and the pipe is hidden by the rocks.


sence justin ran out of space LOL I thought he would throw this in there. that science bleieves that cyano has something to do with the ozone layer I think they said a biproduct of cyano is ozone please correct me if I am wrong please,