Don't know what's wrong with water


Done numerous water changes, checked water with master kit and all came back in normal range. Does anyone know what could be going on? Nothing changed, nothing was introduced to the tank.


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How old is the tank? Are you in the middle of a fishless cycle? What are normal values?
Looks like a bacterial bloom to me, but would need more detail.


It looks like an algae bloom. I would do another water change (at least 50%) and clean the inside of the glass.
Is that sponge filter all you have? What size tank? How about lighting? How much and how long each day?
I have never used one but have looked into UV light for suspended algae in the water. Its designed for the water.
Take a look at this link. Might help you.
Green Water -- Causes and Cures

Don't worry to much as this is very common and easily mitigated. The others here will have much more information for you.


There are two common kinds of cloudy water.
A bacteria bloom is white ish in colour.
And an algae outbreak called green water is green ( surprise)

That looks like green water to me?
Its harmless but will not stop with just water changes. We say algae as in floating algae but it’s more like what I call fresh water plankton. A mixture of plants and animals ( bugs ) .

As it is a food source for tiny fry it can be cultivated deliberately. In order to grow green water you need lots of sunlight and a high level of nutrients.
It stands to reason to stop it multiplying you need to limit sunlight and artificial light. And to lower nutrients.

In my outdoor fire buckets if I let floating plants grow they compete for nutrients. I don’t see a lot of plants in the picture. I suggest frogbit or one of the other similar large floating plants definitely not duckweed.
A maximum of 8 hours lightly. If the summer sunlight is coming in the window of the house at this time of year you could put cardboard on one side of the tank. Something to stop light / sunlight hitting the water.

Feed less. Vacuum uneaten food. Sure do water changes as well.


I agree that it's algae. I've had it happen a time or two in new tanks. Temporarily reducing the light to 6 hours per day and adding more live plants worked well for me. After it cleared up I bumped the light back up to 8 hours per day.


How long do you have your lights on ? Are they on timer? Do you have more than normal natural light coming into your room (because of summer or so, since this can increase the light the tank gets compared to normal) ?

For start you can try complete blackout:
- Cover the tank for 3 days and only feed a tiny bit every day
- Then change 50% water to remove any dead algae
- Repeat process until the green water has cleared up

Then things you can do to prevent it from happening again:
- Reduce lighting period and use a timer (min 6 hours of lights if you have live plants)
- Reduce intensity of lights ( electric tape can be used to cover part of lights if need)
- Add a lighting break of 2-4 hours in the middle of your lighting period
- Don't over feed; feed small amounts and monitor the fish when they eat


I think you have some good answers so I’m just going to say Welcome! I too, am a Baltimore native. But I’m still here! ;D


Ok so the tank has been up for over a year or so..have a cannister filter plus a sponge filter...light is a full spectrum light an run like 14 hrs sun up to sun down. An have ran the tank like these an have had no problem..since the post I did get a uv light for it an is helping but tank still cloudy not as green just whitish



IMO 14 hours of light is way too lonnnggg, lights normally should be 6-10hours depending on what fish are kept in the tank and if there are many plants.

I would reduce the hours down to perhaps 7-8hours each day or if there is no fish leave light of for a couple days so the algae cant grow as rapidally.


I see a window in the reflection from the tank. That will be a contributing factor to the light hitting the tank at certain times of the year.

With 8 hours or less lighting finger crossed the UV helps?


The light is there for you to view the tank. There is really no reason to have them on when your not there. If you had a planted tank, it would be different, but for this tank with a few low light plants, having the lights on for 6-8 hours is more than enough especially with a nearby window.

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