I've noticed recently that the white stones in my fish tank are starting to have something brown growing on them, which I suspect to be mold/algae. The mold/algae also seems to be slowly increasing over time.

  1. How do I remove the mold/algae?
  2. And how do I prevent the mold/algae from returning?


Here is a picture of my fish tank. We have a filter which you can partially see at the back. You can see that the white stones have some brown things on them, but interestingly it only happens on some of the stones. The fish tank also has several brown spots.

enter image description here

  • also what kind of rocks are they? Commented Mar 21, 2017 at 14:20
  • Can you please give some more information about your tank: How big is it, what fish are there, do you have heather and filter, how long is the tank already running, what maintence do you do, do you have real plants in it,... ? Answer to these questions will help in providing a better and more accureate answer.
    – Diether
    Commented Mar 23, 2017 at 16:34
  • @RebeccaRVT Added a picture. Not sure what rocks they are as my mother bought them. Commented Mar 24, 2017 at 8:29
  • @Diether No real plants, though we do have a filter. Commented Mar 24, 2017 at 8:30

2 Answers 2


That could be brown algae.
It often occurs with new tanks, and should disappear after a while.
Make sure you keep doing the regular maintenance.

You can try to scrub it of with your fingers, and then siphon it up while you do your maintenance. Or, if it's harder to remove take the stones out and scrub them with a brush (I've get a toothbrush I only use for my tank). But don't use any chemicals.

Preventing all algae is nearly impossible, but once you have a stable aquarium and regurarly maintain it, you should have less and you should be able to keep it under control.


Not sure why my previous answer about having couple of Bristlenose pleco in the tank was deleted. The point I was trying to make, They clean tank out in no time and keep it clean as long as they are in tank.


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.