Introduction

Pea Soup anyone?

Pea Soup. Lime-Aid. At one point my wife even called it "The Radioactive Tank". I'm talking about "green water", a condition caused by a population explosion of a single celled algae (named Volvox). It grows so numerous that it clouds the water so you can't see the back of the tank! Usually it develops in your tank a couple days before you have important company over. "Ah, so this is the tank you spend all your spare time on... interesting." is usually the comment you will get.

Perhaps nothing in the hobby is more frustrating than having a condition in your tank where you cannot see your lovely fish. It is very easy to obsess about this and go nuts pulling your hair out trying to rid your tank of this infestation of single-celled algae.

The Proper Perspective

If you sit back and think about it, the only real problem that green water produces is an aesthetic one. The fish in your tank don't care one bit how green the water is! In fact, the subdued lighting due to the green water blocking some of the light is probably appreciated by most fish. So we need to put this situation in a proper perspective. Sure it doesn't look good, but the algae is there for a reason. Instead of seeing it as a plague in your tank, you should try to see it as a sign of an imbalance in your tank.

The only real problem that green water produces is an aesthetic one.

As mentioned in the other algae articles, algae control is nutrient control. If there is excess algae, then there is an imbalance of nutrients in your tank. This could be not enough of a particular nutrient, too much of a nutrient, or a combination of both. This is what makes green water particularly challenging, is that it could be a number of nutrients which are imbalanced.

Greenwater Go Bye-Bye!!

This is one of those times where I need to emphasize the importance of having a complete test kit. It's always better to know exactly what the state of your tank is, than to just speculate about the water chemistry and act upon those speculations. It's like flying a plane blindfolded... very dangerous!

Here are some basic tips on what to do in order to rid your tank of the green water. There isn't a sure-fire method guaranteed to work, as it may be a combination of things that finally make the green go bye-bye. Sometimes doing nothing at all will cause the problem to cure itself! The options for you to try are divided into into different sections: Universal Tips, Fish Only Tanks, and Planted Tanks. This is because your options may be different depending on which type of tank you have.

Universal Tips

These options may be tried whether you have a Fish-Only tank or a Planted tank.

• Reduce the light in the tank by amount, duration, or both.
• Reduce the light coming from outside the tank by amount, duration, or both.
• Use a Phosphate absorbing filter media.
• Lower the amount of food entering the tank for a few weeks.
• Lighten the fish load in the tank (less waste).
• Have patience! Sometimes tanks clear up all by themselves without intervention.
• Use a fine media (filter floss) in your filter.
• Do extra water changes if your water does not contain Phosphate.

A Fish Only Tank

When you only have fish in a tank with plastic plants and some other decorations, the options you have to get rid of green water are more 'chemical' and less 'natural'. That's okay, because it can make things a little more simple.

• Turn off the light and cover the tank with towels to block all the light. Keep the tank like this for a few days, then do a large water change (at least 50%).
• Use a UV sterilizer (very effective but also expensive).
• Only use a flocculant (water clarifier) as a last resort.
• Use an algaecide as another last resort.

A Planted Tank

In a planted tank you need to play by nature's rules. Algaecides and a 3-day blackout for your tank may hurt the plants more than the algae. Since algae control is nutrient control (did I say that already?) what we need to do is control the nutrients. This can be done in a few ways, either regulate the amount of nutrients (direct), or lower the chances that the algae will get to use them (indirect).

• Add lots of plants which are fast growers and heavy feeders.
• Make sure there are adequate CO2 levels.
• Make sure there are adequate Nitrate levels.
• Lower the fertilizer dosing for a few weeks.
• Make sure the surface of the gravel is kept free of fish waste.
• Add some floating plants, such as Salvinia, Duckweed, or Water Sprite. (most effective method for me)