So I have had green dust algae on the walls of my planted aquarium for about a year's time, and I have tried a lot of different things, but no matter what, it keeps returning.

I have tried:

  • large water changes;
  • allowing the algae to grow in the tank for at least a month before scraping it off and doing a large water change;
  • lowering daily light duration down to 4 hours per day.

Still I have had no success in getting rid of the algae.

The tank is pretty heavily planted 60 gallon tank, runs CO2 injection, and I use Flourish (weekly) and Flourish XL (daily). Though I have tried halting Flourish dosing, still with no effect.

Any help in getting rid of the algae would be appreciated.

  • Do your plants grow well? If so I suspect an excess of fertilizer. If not, too few nutrient.
    – Rémi
    Sep 1 '16 at 1:03
  • @Rémi Yeah the plants grow well, but I monitor the water weekly and have tried weekly substantial water changes. And still nothing works. Sep 1 '16 at 2:45
  • Do thw tank have direct lighting from the sun?
    – Rémi
    Sep 1 '16 at 10:55
  • @Rémi no sunlight exposure just a finnex light. Sep 1 '16 at 13:16
  • Have you/can you test your water for the basic (amonia, nitrate, nitrite) and phosphate?
    – Rémi
    Sep 1 '16 at 13:18

Try an UV sterilizer.

This will kill the algae in the water. You will still have to do water changes to get rid of the dead algae, but over the space of a week with a few water changes you should have crystal clear water.

What won't work:

Reducing light:

  • Algae need light to grow, so reducing the light would seem like a good idea. The problem is that your plants also need light so reducing the light levels enough to kill the algae would also kill your plants.

Reducing nitrates:

  • Algae live on nitrates. So reducing your nitrates to 0 or near zero would help. However your plants also need nitrates to grow. And even if you wanted to reduce nitrates, you would have to do regular massive water changes to keep the nitrates low enough to prevent algae growth.

Water changes:

  • Water changes will remove some of the algae in the water. But not all of it and there will always be more than enough left to reproduce.
  • I've thought about this but ruled it out because the dust algae is adhered to the tank glass and the water itself is otherwise perfectly clear. In this case will the UV filter be useful? Sep 27 '16 at 17:05
  • It may reduce its ability to spread throughout your tank. In order for it to spread it will need to go through the water at which point the UV filter has a chance to kill it. So it may help with control the Algae and prevent it coming back when you clean it off.
    – trampster
    Oct 10 '16 at 3:50
  • So as I suspected, this does not get rid of the dust algae on the glass, but that being said, on the side of the tank that experiences the heaviest water flow from the filter the dust algae appears to have a difficult time reattaching after I wipe it off the glass. So it seems that water flow rather than the UV light helps with this problem. Nov 11 '16 at 14:23

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