I have found some red algae last night in my tank. I'm looking for possible cause and also a way to kill it. I have shrimp and fish in that tank, so no chemicals if possible.

My water parameters are stable since 4 months:

  • ammonia: 0 mg/l
  • nitrite: 0 mg/l
  • nitrate: less than 5mg/l
  • phosphate: less than 2mg/l.

I do a regular water change once per week or at most every 2 weeks. I use tap water, de-chlorinated, for my water change. I do not dose any fertilizer in the tank and no CO2 injection.

For now all I have is those small algae on an Anubias (see picture below) but I want to find the cause and address it before it does damage.

Here's a picture: enter image description here

  • I found this question here about red algae in a reef tank but it does not look to be the same thing
    – Rémi
    Commented Jan 14, 2016 at 2:30

2 Answers 2


Here's an update on my research and how it went in my tank.

I searched many sources for the cause of those algae and how to kill them. It was suggested to me that red algae appear in high pH water, which wasn't my case (around 7). I haven't found a cause for them to appear.

Here's what I did to remove them: I had quite a bit of brown/green algae on the glass on my tank and I also had many plants hiding a great quantity of snails. Some of those plants weren't as healthy as they could be. So I cleaned my glass as best I could of algae. After that I removed all plants which were not super healthy (this step also removed several snails). I made a bigger water change right after (approx 40% vs my normal 25%). Less than a week after, I made a normal water change (~25%). The red algae regressed by themselves by the next week and as I stand now I don't have any left.

If they wouldn't have regressed I would have used this method I found here on a forum in French (in case you want to read/translate by yourself). The method is the peroxide one. If you resort to this method be sure you are ready to lose some/all your plants. Using a 3,5% peroxide you make a solution 1/9 with tap water (9 parts of water for each part of peroxide) and dip the plant in the solution. The time to leave the plant in the solution varies depending on the plant type. Plants with small leaves are to stay less than 1 minute, plants with normal leaves less than 2 minutes and plants with thick leaves less than 3 minutes. If you are not sure about the plant type, better to underdo it since too long in the solution will kill the plant. Right after the dip, you must rinse the plant as much as you can before you put it back in your tank. The algae will not appear dead right away but over the next couple of days it should start to discolor. As soon as the algae are dead, snails/shrimps/fish will start to eat it (which they wouldn't do normally when it's alive).

  • Very interesting answer! I assume that there is a risk to fish if you're using peroxide on anything in your tank though?
    – Henders
    Commented Oct 25, 2017 at 21:00
  • 2
    Peroxide degrade quickly to ambiance light so by the time you put the plants back in tank the small amount will dilute itself in the water than degrade. Maybe some invertebrates are more fragile but from my research it seem the fish don't mind it at all
    – Rémi
    Commented Oct 26, 2017 at 13:17

Siamese Algae Eaters are one of very few creatures that eat red algae. If you can get a few of those, that might be a way of getting rid of the pest without doing more harm.

There are a few things to consider with this fish, though. They grow quite large, up to 16 centimetres (6.3 in), so a small tank is not suitable for them in the long-term. I have two in my fry tank. They're about 4cm long now, and seem to be thriving. But I know that they will quickly outgrow it and have to be moved into my main tank. Another thing is that they're a schooling fish. The recommendations that I've read is to have five or more of them in a tank. Definitely not suitable for a small tank!

I enjoy these fellows in my tank. They're hardly ever still. Always zipping about. They're doing such a good job that I'm at times concerned whether there is enough food in the tank for them. So I supplement with zucchini slices every so often.

Siamese Algae Eater

http://www.liveaquaria.com/product/1086/siamese-algae-eater https://en.wikipedia.org/wiki/Siamese_algae_eater

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.