Winning the War with Algae

I’ve had a lot of people come to me discussing algae and why plants are good or bad for algae. I wanted to write a comprehensive guide on everything I’ve learned running 30+ high and low tech planted tanks with pretty much every different type of stock, substrate, filter, plants, etc you could imagine. Let’s break it down into categories, starting with the most important.

STABILITY

That’s the biggest word on the page for a reason. Stability means more than anything else when it comes to algae, which most people dislike. The truth is, most just want a quick fix to the ugly green stuff filling their tank- and luckily, there are lots of them! However, the only thing that will truly get you a beautiful algae free tank is time.

A planted tank is not a glass box filled with water and random plants. Your aquarium is a self-sustaining ecosystem. There is far more to what happens inside of that tank than what meets the eye. The most important is the simple cycle of life in the ecosystem, and for that you need light, producers, consumers, and decomposers. In the case of an aquarium, this breaks down to plants and you being producers (because you add food and nutrients to the ecosystem), the fish being consumers, and an army of decomposers made of some fish, snails, bacteria, and microorganisms.

So, science lesson aside, what does this mean for your tank and how you can reduce algae? It’s simple. WAIT. Be patient. Seriously. If your tank is less than 3 months old and filled with algae, it’s probably because the tank isn’t stable. Fully stable tanks can take up to 6 months!

But why does stability matter so much for algae?

What Causes Algae?

Nitrates. Decaying Stuff. Light.

There are three main things that cause algae, with a few outliners. Let’s break them down:

Nitrates. Nitrates are, without question, the #1 cause of algae, and it’s something you should always be aware of. Now, let’s get this out of the way as quickly as possible: If your water test says 0 nitrates, that doesn’t mean you have 0 nitrates in your tank! It means you have 0 nitrates RIGHT NOW, because they’re all being consumed by something. But plants and algae both are consuming it. It’s important to understand that nitrates come from anything decomposing in your tank, including dead plant material, fish waste, floating detached leaves, etc. Pretty much anything organic in your tank that isn’t currently alive will eventually decompose which creates nitrates. This of course assumes your cycle is complete, as they’ll actually decompose and create ammonia, but your filter and cycle will turn all that into nitrates.

Nitrates are crucial to fighting algae, because algae LOVES nitrate. Practically all types of algae need nitrates to grow, but so do plants.

The trick is striking a balance where your plants are consuming so much nitrate that the algae isn’t able to get any of it.

In fact, that sentence is the true key to understanding and combatting algae. Light or anything else aside, if your plants consume all the nutrients and the algae can’t get any of it, then you’ll solve your algae issue.

Obviously, this means that more plants = less algae, which is one of the easiest solutions to algae. Faster growing plants such as floaters consume more nutrients which help tremendously with algae. This also means that more water changes and cleaning = less algae, because you’ll be removing waste and nitrate from your tank with each cleaning.

Decaying Stuff. A commonly overlooked element of algae is where it grows. Algae loves to grow on unhealthy or dying leaves of plants or other decaying stuff, because it’s an easy place to attach, and unhealthy plant leaves don’t funnel their energy to combatting it. Generally, the more dead stuff you have in a tank, the more algae you’ll have- both because they’re decaying creating nitrates, and because they’re creating perfect homes for the algae to grow.

The solution here is simple, clean it all up. I find a surface skimmer works great to help with floating leaves, and I use a turkey baster to blast the substrate or carpet when I do a water change to kick up all the gunk.

Light. There are a LOT of myths related to algae and light. I’m not a scientist, but I’ll explain what I understand and what I’ve found with my effort. No, blue light doesn’t cause algae. Yes, light DOES cause algae. But no, turning down your light for a few days won’t magically fix your algae issue.

Let’s explain. Light works in spectrums, and for aquarium lighting the three main colors of Red Green and Blue matter the most. I’ll be writing a blog post on lighting soon, but in general remember blue light helps plants grow, red lights help plants color up, and green light makes your tank not look like it’s purple and balances it all out.

Now, if you think about that, technically that means green light is useless, and in a lot of ways it is, you can grow plants perfectly well with just red and blue light. If you’re looking to make a quick adjustment to your lighting to reduce algae, try turning down the green light a good bit.

Algae needs light to grow just like plants, but it isn’t as picky about spectrum as plants are. As long as it has light, it can grow, and naturally more light means more algae just like it means more plants. With this in mind, an important note is that more light does not necessarily mean more algae. This is another very common misconception. Theoretically, in a perfectly stable tank where the plants consume 100% of the generated nutrients, you could light your tank with a light as bright as the sun and still not grow algae. As I mentioned before, algae NEEDS nitrate to grow, as well as other stuff. If the plants are already healthy and consuming all of it, algae can’t grow.
However, light perpetuates algae issues. If you already have a lot of excess nitrates from an unclean or unstable tank, blasting it with light will absolutely give you loads of algae. And, inversely, since algae does need light to survive you will slow down or kill algae growth by turning off the lights. Just remember that without fixing the underlying issue of nitrates, the moment you turn your light back on you’ll be back to square one.

Other stuff. There ARE other factors that influence algae. One important one is silicates. Algae cell walls use silica, which isn’t usually found in aquarium stuff, so if you can reduce silica from your tank it’ll help algae. Seachem PhosGuard is great for reducing this and phosphates. This is why most aquarists will recommend you never use play sand for a tank’s substrate, because play sand is full of silica. Pool filter sand is much better. Phosphates have also been linked to algae growth, but they’re also important for plants so it isn’t advised to try to remove all phosphates.

How to fix algae issues

What you’ve all been waiting for! Here are some tips on how to fix algae issues, once again in order of importance.

Wait. Seriously. Be patient. Your brand new fish tank isn’t going to look flawless a month after making it.

Clean your tank. A lot. Vacuum your gravel, use a turkey baster to kick up more gunk. All the decaying brown stuff in your tank is decomposing and creating algae.

Reduce feeding and nutrients. Food turns into poop which turns into nitrate which turns into algae. Less food means less algae.

Improve filtration and flow. A better filter makes a tremendous difference in fighting algae. More flow and biomedia means water isn’t stagnant and it can be filtered more efficiently as well as keeping plants healthier with more gaseous exchange. I always recommend a filter at least 2x the size of the tank: A 10g tank should use a filter meant for 20g tanks. I really like these rebranded SunSun filters, which not only include really nice media but also a UV light* and a surface skimmer. amzn.to/3rrWRzI

UV. UV filters/lights are great for preventing cloudy or green water. If you’re having an issue with your water being endlessly cloudy or green, get a filter with UV or a small UV light to add to your filter and it’ll clear up in a few days. I keep a small one handy for anytime a tank turns green.

If you’re using disposable filters… STOP! Those disposable filter cartridges are just ways for companies to steal your cash, and they’re awful for your tank. Every time you throw one away you’re throwing away all the beneficial bacteria who can help break down nitrates. Just shove a cheap sponge in your filter and you’ll be fine.

Anaerobic Bacteria. There’s a special type of bacteria called Anaerobic bacteria that grow where there is no oxygen, and they’re the best for actually reducing nitrates (as opposed to aerobic bacteria who reduce ammonia and nitrite). Good biomedia like Seachem or Biohome add more space for anaerobic bacteria, and deeper substrate does as well. Generally, more biomedia = less algae.

Algaecides. The stuff with copper in them don’t work, don’t try. Truthfully the only one I’ve found that actually makes any discernible impact is Seachem Flourish Excel, which is very effective at killing algae if dosed daily, and it isn’t toxic for shimp and snails like the other algaecides are. Excel is also great for spot treating blackbeard algae, I use a syringe with a long needle at the tip.

Clean your tank again. I mean it. Nothing else here matters if your tank is still full of literal crap decomposing and filling the water with nitrates. And remember, just because you don’t have any nitrates on your water test doesn’t mean you don’t have stuff decomposing- algae is just probably already using it.

Less fish. Fish generate waste, and more fish means more waste. Plecos and snails generally make algae WORSE because while they do eat algae, they also generate waste which makes more algae. If you’ve been struggling with algae and can’t figure out why, try taking some fish out. Shrimp are some of the only creatures that effectively have a negative bioload and will 100% help your algae issue more than hurt it.

More plants! This is one of the most important. Plants absorb nitrates so algae can’t. Adding more healthy plants from Sunken Treasure Aquatics will not only make your tank prettier, but help reduce algae. Fast growing plants such as floaters or pearl weed are great for absorbing loads of nutrients. Floaters are especially effective at fighting algae because they grow incredibly quickly, consume tons of nitrates, AND block out some of the light.

Embrace it. Sometimes algae just looks nice, and it almost never hurts your fish (though it can hurt your plants by blocking out light). I often leave blackbeard algae alone and in some cases just leave algae alone in general. Obviously this is entirely your decision and not a solution, though.

Hopefully that helps, and please do feel free to ask if you have any questions!