[seattleguthries]

My planted 20 gallon tank has been established for about 6 months now. I run pressurized CO2, fertilize regularly and have 48 watts of T5HO lighting. I have a HOB filter with standard filter media and purigen.

Lushly planted tank is thriving, as are fish.

About three months in I had an attack of green water algae. At that time I used Diana Walstad's advice (Ecology of the Planted Aquarium) to use charcoal, introduce water lettuce and decrease the use of full spectrum lighting, her theory being that iron is the limiting factor. This cleared it right up overnight.

Three months later I am using a similar strategy this time but am not seeing my green water problem clear up as quickly. The planted tank guide on this site suggests that I do nothing and that the algae will eventually "burn itself out" in a week or two.

Any advice is greatly appreciated. Thank you.

 

[Complexity]

The best way to clear it up quickly is to use a uv sterilizer. The water will usually be sparkling clear in only 2-3 days.

For those who prefer to wait it out, it has been known to go away on its own. The longest I remember following someone who used that method took about 4 weeks. Generally, 2-4 weeks is about normal, IIRC.

However, there are some cases in which the green water persists for may months. If that happens, then more will have to be looked at to see what's causing it. It's a rare enough event, it's not something I would worry about at this point.

The good news is no matter which way to decide to go, green water is not harmful to your tank inhabitants. The only problem may be that it blocks the light to your plants. And, of course, it looks ugly as heck. But it's not killing your fish or inverts. They're just fine even if you do wait to let it clear up on its own in a few weeks.