Maintaining a healthy tank/preventing cyano has many considerations. If you have a small/simple setup, just do regular tests/water changes and just skip to TL;DR for the immediate cure.
What causes Cyano(bacteria)?
Cyano growth is driven by many of the same factors that promote algae growth. The most common is overfeeding. Fish food and waste introduces phosphates (PO4) and organic nitrogen compounds (henceforth referred to as ONC), which are initially broken down to ammonium compounds (ammonification) into your tank. If nitrifying bacteria
are present -- most often introduced on live rock, but now comes in a bottle with mixed success -- they'll perform a process called *nitrification
; which is roughly converting Ammonia/Ammonium (NH4/NH3) → Nitrite (NO2) and Hydroxylamine (NH2OH) → Nitrate (NO3)
. Denitrifying bacteria must then convert the nitrates into free nitrogen (N2
), which is dissipated through surface agitation. This and other processes are referred to the all inclusive term, the
Natural Method 1: Plants
Plants and algae uptake these same compounds (as well as phosphates) and process them in reverse order (assimilation), but instead of releasing free nitrogen they store ammonia and phosphate for growth; as well as turning carbon dioxide into oxygen (CO2
- Noticed the compounds in the above nitrification process. Each contain more oxygen than their predecessor. Couple that to the fact that you have your fish also breathing the dissolved oxygen. Anything wishing to utilize the ONC will have to compete for these resources and cyano thrives in low oxygen water. Therefore, higher oxygen content will increase competition and hinder cyano growth.
- Surface agitation is the most efficient way of increasing dissolved oxygen. Some such ways of accomplishing this are mechanical filters, the gravity drain into a sump, or a bubbler.
Natural Method 2: Macro Algae
Macro algae is my favorite method of Nitrate control. It not only works well, but the right type is the favorite food of many fish. Since they do accumulate phosphates and ammonia, it's recommended you cull the macro every so often to manually remove these elements from the tank. Additionally, you macro has no room to grow, it will no longer be using up the ONC you're trying to get rid of. If you do opt for the type of macroalgae that your fish like to eat, you may need to grow it elsewhere, like a sump or you won't have it long. But realize that some macros drawbacks: Some aren't as good at exporting nutrients, some are invasive, fish won't eat all algaes, etc.
A protein skimmer is one of the best methods of controlling organic nitrogen. It helps remove fish waste and excess food before it has a chance to ammonificate. Other chemical and mechanical filters also exist, but I don't use them much so I won't speak on their behalf. If I get a media reactor or ozonator I'll update. Protein skimmers also have the added benefit of surface agitation, aiding in dissipating free nitrogen as well as dissolving oxygen.
Work great for removing all sorts elements from your tank. They work a little too well and are bad for anything requiring trace elements. I avoid carbon like the plague.
There are many organic mediums that do the same job as nitrifying bacteria, helping the process along.
Equipment: Power Heads
Large tanks with poor circulation can suffer from pockets of built-up ONC called dead spots. Power heads are pumps that circulate your water to allow efficient removal of ONC, with the added benefit of fish exercise, feeding filter feeders, and regulating consistency of temperature/pH/salinity.
Maintenance: Proper Lighting
Old/poor lighting also promotes algae and cyano growth. Grow bulbs have a spectrum that extends beyond the visible to where most plants photosynthesise (UV). After 6-12 months (depending on the type of lighting -- LEDs will can last much longer), the bulbs should be replaced as their spectrum will likely have fallen below what your plants require; anything needing this spectrum of light to photosynthesise won't be nearly as efficient at processing the nitrogen and of course algae and cyano have no problem using this spectrum.
Maintenance: Proper Water Conditions
Improperly filtered water is full of all sorts of compounds that detrimental to your tank. Tap water usually contains phosphates, nitrates, copper, and many other things you don't want -- especially
A few people claim certain animals will eat cyano. I have never had success with this, but I can't say I've tried too hard. The thing to remember that even though cyano is often called blue/green algae, brown algae, [whatever ugly algae], it is actually bacteria. It is thought to be toxic for many that try to eat it, but I'll stop the conjecture at that.
What You Should Be Doing
The biggest culprit is over-feeding. Only throw a little food in at a time. The extra that falls to the bottom is often not eaten and just pollutes the tank. Avoid the temptation to over feed. Smaller feedings 2 or 3 times a day is preferred over a large feeding once and never more than they can consume in a few minutes. Also, more nutrient-dense food will pollute the water faster.
Get Yourself Tested
Test often, especially if your tank is young. A routine water change is often the preferred method of removing nitrates. If you have nitrifying bacteria, you're limited on how often you can do a water change. Otherwise you run the risk of reducing your bacteria to critical levels (see tank cycling). Many mature tanks only need 10-15% change every 2 weeks; I do %20 once a month and that's only as an alternative to dosing my corals. If you have certain parameters really out of whack, you should be able to get away with 10% every 3 days for a few changes. This is only a general rule of thumb and will vary widely by the efficiency of your filtration, the type of animals in your tank, and your experience in dosing. Just be careful to do match the parameters of the water coming in.
pH plays an important role in your bacteria's ability to function
See the Warning Signs
For most people algae is inevitable and to a degree even somewhat beneficial by providing oxygen, food, and denitrification. It's a strong competitor (most of the time out competing cyano and everything else). Keep an eye on this one, it's a great early warning of excess ONC. In my opinion, the best thing about algae is that it's an excellent early indicator of your parameters getting out of control.
Surface agitation, while helpful and completely necessary, also introduces CO2 from the atmosphere into your tank - encouraging algae growth and lower dissolved oxygen. The air in your house (depending on where you live) will have higher CO2 than outside. For this reason, some people opt to pull their tank's air intake from outside.
The Cure (TL;DR)
So now that I've covered the basics of avoiding cyano, what to do now that it's a problem? If you don't have anything photosynthetic (I know you have plants but I just want to cover it), you can "black out" your tank. That's when you completely cover the tank and allow NO light in. It doesn't bother the fish much and will kill the cyano.
Antibiotics are quite effective at killing cyano as well. I'd recommend you remove as much of it manually as possible first. Turn off your pumps and start scraping with a siphon right behind. The antibiotic is going to leech oxygen from your water, so increase your surface agitation (ie add a bubbler). The antibiotic usually takes 24hrs to work, so be ready to do a large water change immediately after (I go for 20%). If you have a protein skimmer, it's going to go crazy for the first few hours. This is normal, just stay on top of it.