green water woes - The Planted Tank Forum
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post #1 of 3 (permalink) Old 06-16-2004, 06:55 PM Thread Starter
Algae Grower
Join Date: Feb 2004
Posts: 23
green water woes

I have been battling green water in my tank for the past 2 months. turning the light off for a few days does the trick but once it goes back on it comes back. My plants seem to be dying slowley as well. I have a 40 gallon with a 90 watt aqualight and very few fish. I got my water tested today and everything is fine. nitrate was at .10 i think and ph and hardness were all normal. Im using CO2 form a hagen system. they didnt have a test for phosphates so should i assume that is the reason. If so...should i raise my nitrate or decrease the phosphate?

ANy help is appreciated.
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post #2 of 3 (permalink) Old 06-16-2004, 08:18 PM
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Join Date: May 2004
Location: Houston, TX
Posts: 10
Like you I am an "Algae Grower", but I'll try givin it a shot. The more experienced guys can correct me if I'm wrong, which may be very likely.

I believe green water is pretty common in new setups or when lighing is increased dramatically. Green water thrives on the nutrients free in the water column.

This may be a successful procedure to rid green water if you haven't tried it already:

The best thing to do may be nothing at all, quit all ferts and allow the algae to consume all valuable nutrients. Also, cut back on the amount of food you feed the fish. I think fish flakes contain high amounts of phosphate? If I am thinking correctly, this should result in a dramatic decrease in suspended algae, sort of a self termination. From the sound of it, the plants are probably suffering most from the lack of light penetrating through the water. Most plants are fairly resilient and can go without dosing for quite a while.

How old is the setup? If the setup is only 2 months old, I'd hold of ferts until the plants get better established. This is usually only a few months or until the new plant leaves grow in a yellowish color.

If this technique works, do a 50% water change once the water is clear. If there is no "bloom" after the water change, start dosing in very small quantities if plants ask for it, and increase dosing slowly over time to the recommended parameters.

I hope this helps. Does anyone agree or disagree?


75g,UGF & Fluval 404,1.7wpg, pH 7.2,fish poo ferts (FPF)
-Rubin Swords,Spiral Val,Crypt wendtii,Dwarf Red Lily,Aponogeton crispus
-Festivum,3 Angels,5 Rainbows,5 Ottos,3 Corys,10 Tetras
20g,UGF,1.0wpg,pH 7.2,no ferts
-java moss on wood, rock and 3" pot
-separation/quarantine/hospital tank
10g,Fluval 303,DIY co2,3.0wpg,pH 6.4-6.6,KH 5-6,no ferts
-Spiral Val,Crypt wendtii,Dwarf Red Lily,Aponogeton crispus,Red Ludwigia,
Cardamine lyrata,Lobelia cardinalis,Limnophila aquatica
-1 SAE,4 Amano Shrimp
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post #3 of 3 (permalink) Old 06-16-2004, 08:55 PM
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Join Date: Jul 2002
Location: Victoria,British Columbia, Canada
Posts: 3,461
You should try to find balance in your tank... I cant tell you to raise or lower one thing or another without knowing what they are. You want to achive a 10:1 ratio for Nitrate and Phosphate (10 parts Nitrate to 1 part phosphate) if that ratio is out of whack in one way or another that could explain your algae trouble.

Green water can be a royal pain to eliminate. In some cases it goes away on its on, "burning out" as Jesse mentions... However in other cases it can be far more stubborn and problematic. I had to use a UV sterilizer to eliminate my Green water... and others have used Diatom Filters with great sucsess.
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