While owning a pet in an aquarium is great, maintaining it can require a lot of work. If you’ve ever noticed black spots on your aquarium glass, you have probably wondered what they are and how they got there. In today’s article we will cover everything you need to know about brown algae spots on aquarium glass.

What are the brown spots on my aquarium glass?

Brown spots on aquarium glass are called brown diatoms. They usually grow on aquarium glass, but can also grow on plants, substrate, or any other surface in your aquarium.

They are very similar to algae, and some people just refer to them as brown algae. Luckily, they can easily be wiped away with a towel or rag.

What do they look like?

Brown diatoms, or brown algae, usually starts as a small circle on your aquarium glass. While it is usually brown, it can also be an orange or red color. Sometimes, it can even look like rust on your aquarium glass.

Most of the time, these brown spots will form in groups of small circles on your aquarium glass. However, sometimes they might just be circles by themselves.

Below is a picture of both types of brown algae.

What causes brown algae spots to grow on aquarium glass?

Brown algae spots grow in aquariums when there is excess phosphate and silicates. This is almost always a result of using tap water for your aquarium.

While you can certainly use tap water for your aquarium, it is very important to condition it first. You can learn more in my article on how to make tap water safe.

Brown algae spots can also appear at the end of the nitrogen cycle, which occurs a couple days after you put water in an aquarium. You can learn more in my guide on what causes algae in turtle tanks.

You can help prevent brown algae in the future by using a turtle cleaner conditioner.

If they keep coming back, I recommend that you do a full water change, as demonstrated in my below:

How to get rid of brown algae on aquarium glass?

Luckily, it is very easy to remove brown algae from aquarium glass. All you need to do is wipe it away with a clean rag. It is important that you make sure that the rag has not been exposed to any sorts of soaps, as this can be toxic to any turtles or fish that you have in the aquarium.

You can also use an algae scrubber or a brush. Just make sure that you do not push too hard so that you don’t scratch your aquarium glass.

While brown algae usually disappear after a week or two when it runs out of food, I suggest you remove it right away to prevent it from spreading.

If your aquarium water has a yellow/brown tint, it might be cause by tannins.

Are brown algae dangerous for my turtle or fish?

Luckily, brown algae are not dangerous for either turtles or fish. Even if your turtle or fish starts to eat it, they are not toxic.

However, brown algae can spread fast, which can make it hard to see through your aquarium glass. It can also cover your ornaments, so I suggest you get rid of it as soon as you notice it.

Additionally, if it starts to take over your tank, it could cause your aquarium plants to stop growing.

How to prevent brown algae in the future?

Luckily, there are many ways to prevent brown algae growth in the future. These include frequent water changes, live plants, appropriate feeding, strong filters, avoid tap water, and algae eaters.

Frequent water changes

This is the key to preventing brown algae in your aquarium. Frequent water changes not only diluting excess nutrients in your water, but it helps prevent your water from becoming cloudy.

I also suggest doing a thorough cleaning of your substrate every couple of months, as these can also be hosts to brown algae growth. To learn more, check out my article on the best way to clean a turtle tank.

Live plants

Live plants eat the same nutrients as algae. Therefore, if you have enough live plants in your aquarium, the algae won’t have any nutrients to feed on. If you want to learn more, check out my article on the best live plants for a turtle tank.

Appropriate feeding

When you overfeed your turtle or fish, the excess food floats to the bottom. It eventually decomposes and then converts to nitrates and phosphates, which is what brown algae feeds on. Therefore, you should only feed your aquarium pets as much as they can eat, and nothing more.

Strong filters

If you’ve had a turtle or fish for a long time, you know how important a filter is. If your aquarium keeps experiencing algae growth, there is a chance your filter is not strong enough. If you suspect this is the case, you should get a stronger filter. You can also try switching out the filter media, as this can help limit brown algae growth as well.

If you have a turtle, you should check out my article on the best turtle tank filters.

Avoid tap water

As I mentioned earlier, it is perfectly okay to put tap water in your aquarium as long as you condition it first. However, sometimes a conditioner doesn’t do its job, or a tap water is extremely high in phosphates or nitrates.

If this is the case, then I suggest you try putting in distilled water. If you have a big aquarium, this might be expensive. Another alternative is to purchase a reverse osmosis water filter, which removes toxins from water.

Algae eaters

If you have tried everything and your brown algae still appears, you should look into getting algae eaters. Some of the best algae eaters for an aquarium include suckermouth Plecostomus, molly fish, and rosy barbs.

You can also look into getting algae eating snails or fish.  If you are looking for other ways to improve the aesthetic of your aquarium, you should read my guide on how to remove trim from aquarium.