Green water in tank - cant get rid of it

By: erik11
April 6th, 2010
6:22 am

Green water in tank - cant get rid of it

I have a 70 gallon freshwater tank. It was great the first 5 months with just fish, no plants in it. Somehow I got an algae bloom in my tank and now my tank has been green ever since. The fish have all been fine, but its just hard to see them. Here's what I have done to it and my tank parameters:

Water quality: Ammonia, Nitrite, Nitrate, PH, Alkalinity, Hardness, Chlorine, all zero or in normal zone
Tested for Phosphates: 10.0+ obviously it was off the scale
My tap water had 1.0 phosphates in it already
Added a few plants to help with the phosphates - no change
Aeration: 2 bubblers which I turned up to increase air in the tank - no change
Filters: 2 Outside filters and one Under gravel filter tube with power head
Temp: 80
Water changes: 50%-66% weekly! but the green comes back
I have two 20 gallon tanks using the same water and they are not green at all

Chemicals used: Algae fix (didn't help), Microbial Algae clean (didn't help), Algae Destroyer (didn't help),
What did seem to help was the combination of: Phosguard or Phospure in one bag, while I put a Poly filter in one of my filters. This cleared the tank of phosphates in a day, left a white cloudiness, but then after a week, I assume the poly filter was full, and the green started coming back.

I bought a bunch of poly filters, but by themselves, they don't work. Its way too expensive to buy phospure, phosguard, and polyfilters to clean the tank and/or make weekly tank changes.

There must be a way to clear the tank so I can have normal clear water like my other tanks and only make monthly water changes.

I am about to drain the tank and start over!


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34 comments on "Green water in tank - cant get rid of it"

  • Jay
    April 6, 2010 at 11:09 am

    Hey Erik...Welcome to the forum

    It is not clear to me, reading your post, if the water is green, the glass, or both? I would step back from the algae killers, they also kill fish and inverts.

    Not to soon as we know what algae we are dealing with we can get rid of them quickly.

  • erik11
    April 6, 2010 at 2:30 pm

    I have minimal or no algae on the glass or my rocks, etc. Its just in the water.

    Also, I bought new light bulbs, one 50/50 blue/white and the other a regular white aquarium bulb, not the cheap home depot bulbs.

    Also, I only keep the light on 10 hours out of the day and there's no direct sunlight into the tank.

  • Jay
    April 8, 2010 at 4:51 am

    Green water is a very common aquarium problem, it is also one of the more difficult to overcome. The bloom of the organism involved is caused by high phosphates, ammonium, and or nitrates. The organism can and does rapidly switch from one nutrient source to another. It reproduces at a very rapid rate so water changes are of little use.

    How to beat it back...

    You may want to cut your light back to 8 hours. You did not mention the watt rating or type of tubes you are using.

    Do you vacuum your substrate thoroughly when changing water? If not, you should

    You are going to have to find a way to scavenge up the PO4, a few plants are not going to help at your level. Your nitrates need to be at 10 or below.

    A diatom filter will clear the tank in a few days.

    A UV filter will wipe it out and keep it out.

    A big pain, but cheap, is a 72 hour complete light blackout. This critter uses photosynthesis and three days in complete black will kill it along with other green algae.

    Be careful not to cross contaminate your other tanks.

  • erik11
    April 8, 2010 at 5:50 am

    Thanks for the advice. I plan to change my bulbs since another person told me they were part of the problem as well. Right now, I have my tank in blackout mode and will also look into the UV filter option if the new light doesn't work out.

    I will also do a more thorough job on cleaning the substrate to keep my Nitrates down.

    Thanks a bunch!

  • erik11
    April 13, 2010 at 2:17 pm

    OK, here's an update on my green water problem. I changed my bulbs to cool white - non plant/aquarium grow bulbs & non-actinic. I know the color spectrum has a lot to do with growing algae, but I'm not sure what spectrum these bulbs are or what I need to buy.

    Also, I reduced my light-on period to only 3 hours a day, removed my UGF, and did a 66% water change. The fish are still fine and the water quality is all normal, but the green water still grows.

    I decided to buy an UV sterilizer/clarifier. I was planning to buy this one:

    Is this a decent UV sterilizer? and what kind of power head/pump do you recommend.

    I would rather not spend hundreds of dollars if I can help it. Can anyone recommend anything?


  • Jay
    April 13, 2010 at 4:36 pm

    hey Erik

    There are a few submersible UV available out there. I will try to find you a link. Much less expensive and way easier to use and plumb. If you decide to go with UV, I would advise a 100% 72 hour blackout preceded and followed by a 50% water change.


  • erik11
    April 13, 2010 at 8:37 pm

    Thanks for the Link Jay. Does a 100% blackout mean covering the tank or just keeping the room as dark as possible with a little resident light coming from the other rooms?

    Also, I read that I would have to have a 15watt sterilizer if I ever decided to use it to kill parasites. I figured I should go ahead and get at least a 15watt unit. Will this 13watt unit do the same thing?


  • Mister Sparkle
    April 15, 2010 at 1:07 pm

    I'm just dying to's the water?????????

  • erik11
    April 15, 2010 at 2:32 pm

    Its still green. I'm waiting for a UV filter/clarifier to come in to set that up and clear up this whole mess.

    Our water has more phosphates in it than any other water where I have lived before and seems to grow green water real easy. I don't have the right spectrum of light bulbs and am getting fed up with the trial and error thing.

    Once the UV filter is set up, I'll let you know how it goes.

  • Jay
    April 16, 2010 at 2:55 pm

    Erik...stop futzing with the lights, the algae we are talking about here will grow under very low light conditions. A blackout to kill green algae, is just that, a 100% complete absence of light. You can cover the tank with heavy duty black vinyl lawn and garden bags. 72 hours is the key.

    Again, you will need to deal with the phosphates! I am a planted tank guy and dose my tanks 2-4 ppm PO4, but in an tank with only a few plants that would be an invitation for an algae bloom. You might consider a RO filtration system for your tap water if you think scavenging chemicals are too expensive.

    Losing the UGF is a good move, they can be nitrate factories.

    Yes a 13 watt will do the same thing.


    Lights...Compact Florescent equivalent no more than 140 watts 7-8 hours a day

    Chemistry...PO4 at trace levels, NO3 as low as you can get it...10 ppm

    Run a UV sterilizer or Diatom Filter.

    Start the attack with a through filter cleaning and sanitizing...fifty % water change...72 hour complete light blackout - No Peeking NO light!!! ...another 50% water change.

    The tank will be crystal clear after the blackout, but, the green guys will return if the other steps are not taken.

    You might also want to consider a planted aquarium to take advantage of your water conditions. Sorry for the terrible picture, but you get the Idea

    This tank eats nutrients quickly and has no algae issues.

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