Biofilm is a common issue to planted tanks — I’ve seen the issue in my own tanks, as well as others’ aquariums.
In fact, for this article I’ve actually intentionally caused a heavy biofilm in one of my own tanks—just to show how these steps work.
So if you just want to eliminate it (and keep it from coming back), here are the exact steps to solve biofilm in your planted tank once and for all.
Let’s get started.
- Step 1: Understand What It Actually Is
- Step 2: Prevent Biofilm Buildup
- Step 3: Increase Flow
- Step 4: Check Your Dosing
- Step 5: Reconsider Your Food Amount
Step 1: Understand What It Actually Is
Here’s the deal: there’s a lot of confusion about what’s in biofilm. Here’s the technical definition:
What is Biofilm?
Generally speaking, biofilm is the carbohydrates and lipids from organic waste produced in a planted tank. The ‘film’ is produced by bacteria feeding on the excess organic waste present in the water — and that organic waste can come from livestock and plant life in the tank.
In regular-people terms, that means biofilm stems from organic waste — the ‘stuff’ that’s given off by fish and plants. Unless you want to remove all the fish and plants from your tank, we can’t eliminate the source of the organic waste.
But we can mitigate the effects of that organic waste:
Step 2: Prevent Biofilm Buildup
Biofilm only forms when organic waste builds up past “background” levels. If you prevent it from ever reaching that point, it’ll never form that thick surface layer in your tank.
The most effective (and easiest) method of preventing biofilm buildup is using a surface skimmer.
Skimmers used to be a “saltwater-only” item, but in the past decade the industry has learned that the biofilm buildup can be bad for freshwater tanks, as well. (It reduces the efficiency of gaseous exchange, i.e. your water has less oxygen.)
There are numerous options for skimmers:
Standalone solutions work best, but anything that agitates the water surface (and preferably pulls the water itself into the column, à la lily pipe) will do.
Your primary goal is to continually remove any trace of excess organic waste present at the surface. If there’s no waste, there’s no bacteria — that means no biofilm.
There are other significant benefits to skimmers (like increased oxygen concentrations and better CO2 distribution), but skimmers aren’t for everyone.
If you have a smaller tank, or simply don’t want the extra equipment in your tank, a surface skimmer isn’t your only option:
Step 3: Increase Flow
Since that organic waste buildup at the surface is what we’re trying to prevent, increasing the flow in your tank also alleviates the occurence of biofilm.
Your tank’s filter should generally be at least 10 times the volume of your tank.
That’s enough flow to ensure the entire column of water in your tank is being circulated. In nearly any standard tank, a filter with GPH greater than 10 times your tank size is enough to keep the surface agitated and allow minimal organic waste buildup.
Your filter intake/outflow can further agitate the water to continually ‘breakup’ that waste. (As we mentioned already, lily pipes are a great choice for this.)
Conveniently, high flow in a tank also drastically reduces “dead spots”, or stagnant, still areas of water. (This helps — again — with oxygen concentration and CO2 distribution in your tank.)
We’re creating a microhabitat in our tanks, so it shouldn’t be surprising that everything is interrelated!
Step 4: Check Your Dosing
Most biofilm comes from the buildup of organic waste.
However — if you’re using fertilizer in your tank, there are rare cases where that biofilm could actually be iron bacteria at the surface, feeding on the available iron in your water. (This is commonly seen as a “silver-like film” on the water surface.)
Depending on your plant needs, consider whether you can reduce your dosing, or changing the amount of available iron in your fertilizer.
Also consider swapping to a fertilizer that’s more biologically available, to reduce the amount you actually need to put in the tank. (I use Tropica Specialized, but I’ve had success with NilocG ferts historically.)
In other words, if “more” of your fert can be used by plants, you can reduce the amount you’re adding and still get the same growth results.
This is easier if you dry dose or dose separately. For those using a “complete” fertilizer, there are few options other than simply reducing the fertilizer amount overall.
In some cases, improperly managing your water parameters can cause organic waste buildup. (i.e. you’re adding too much/too little ferts or minerals.) More on that here.
Step 5: Reconsider Your Food Amount
Fish food of any kind contains proteins. (Or at least it should.)
When you add more food than is “used” (eaten), you’re directly contributing proteins, which is the number 1 contributor to the organic waste in a tank, and can directly cause biofilm itself.
In addition, as your food decays and releases oils and other byproducts, that also contributes to the biofilm buildup.
Normalize your feeding times and make it consistent. This does a few things:
- Anecdotally, it can “train” most fish to eat more food at the time it’s provided
- Gives you more context to actually see what is (and isn’t) eaten by your livestock
- Makes it easier to see in your water testing whether food is contributing to ammonia buildup
- Results in generally-healthier fish
You’re probably quite a busy person — I am, too! I don’t have time to measure and dose food to each of my tanks.
Thankfully, there are solutions for this, and you’ve probably seen or used them before: auto-feeders.
As cheesy and dated as they appear, they’re a great solution for making your feedings consistent. (I’m a fan of the regular ol’ EHEIM versions — you can see them on Amazon here.)
Now It’s Your Turn
And now I’d like to hear from you:
Do you have any questions about biofilm?
Maybe you have an alternative solution that I didn’t include here.
Either way, let me know by leaving a comment below right now.