I have these brown algae all over the plants and I don't know how to get rid of them.

Any tips?

I would use Seachem Excel to get rid of it. You may need to trim back the plants to reduce the amount in the tank. I use it weekly to keep this kinda stuff away.

Kill the lights, put a put a sheet/towel over the tank, stop feeding. Check every day. Algae should clear up.

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I would follow this advice. Too much light and/or nutrients lead to a brown algae problem the Seachem Excel is a chemical form of CO2 and might enhance the brown algae growth not inhibit it. RO water and a UV sterilizer will also help.

Seachem Excel does wonders for Black hair algae. When I first started my 75 I had my Glo light on for like 12 hours a day and had a huge problem with it. I over dosed the tank with Seachem Excel and it all died off in a few days. The other plants did suffer a bit, but I didn't lose any.

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75 Gallon Planted

Here is Seachem's take:
"Q: When I first dosed my tank with all the Flourish products I was experiencing quite a bit of hair algae. Within three days the hair algae had turned a reddish orange and about four days after that it had completely disappeared. Do you have any idea just which of these products could have caused this? I must admit that I have never seen such a dramatic change with the algae when I first used the Flourish products, and I would really like to be able to repeat the experience when ever the algae re-appears.

A: This is a known side effect of Flourish Excel that may sometimes occur. It has been reported to us by other consumers, however it does not occur under all conditions therefore we do not promote it or sell it for that purpose."

I believe some of the main cause for algae growth are excessive lighting (duration and/or amount), excessive nutrients and poor water quality. I guess I would not be inclined to overdose the tank to fix one problem.

my $.02

That looks like the stuff my nerite snails love, they clean it right off the leaves and everything.

Thanks for the replies guys. I guess I will try the lights out first before adding chemicals. How many days should I go without lights and food though? Also, how stressful will that be for the fish?

PS: I do weekly water changes and water tests and water is fine. I have lights on 10 hours a day. I did run CO2 for the past couple of months and was adding plants fertilizer weekly. Plants were growing nicely... but so did the algae.

Lighting is not necessary for fish, it is for us and plants. For us so that we can see the fish for the plants so that they can grow. By turning off the lights you won't stress your fish out at all. Most fish can go a week or more without food. So chances are your fish will not go under too much stress through this process.

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I've never seen a blackout work for that type of algae, but it may.

What size tank? What light is on it and bulbs? How long do you leave it on? How long has the tank been running?

Aquarium is 3 and a half months old, 21 litres (5.5 gallons), lighting 1 x 8 Watt T5, light was on 10 hours a day.

I know I already said it but I do recommend olive nerites for this type of algae. I had a 30 gallon tank that looked like yours I added 10 nerites and it was gone in three days, even the plants were clean. I'm not a fan of algae eaters as a cure all but in this case it worked great. They won't eat hair algae though.