My Fish Tank Water Turned Green! How to Make it Clear Again (Easy Fix)

Is your fish tank water green? Here I will show you ways to get rid of the green water in your aquarium and how to make the water clear again.

Why is My Fish Tank Water Green?

It’s definitely not normal to have your fish tank water turn green. The reason why your fish tank water is green is a result of a sudden proliferation of algae growth. Usually this uncontrolled algae growth in your aquarium is a result of too much light. It can also be a result of too much organic waste in the water.

I remember the first time I ever saw out of control algae growth. It was very disturbing to see the water in my 10 gallon aquarium turn green! I panicked! I knew immediately something was wrong.

Fortunately, it was an easy fix to get rid of the algae. In no time, the water in my fish tank went back to crystal clear. And I’m happy to report that no fish died in the green water!

Fish Tank Water Turned Green as a Result of Too Much Light

One of the reasons why your fish tank water turned green is because of too much light. Too much light can cause an overgrowth of algae which will turn the water green. Perhaps your aquarium is next to a window and getting sunlight all day long.

Fish Tank Water Turned Green Because of Too Much Organic Waste in Water

Another reason why your fish tank water turned green is because there is too much organic waste in the water. This is a result of overfeeding or decaying plants. It can also be a result of infrequent water changes, too many fish in the aquarium or a dirty filter. All this can lead to too much organic waste in the water which will result in an overgrowth of algae and your water turning green.

How to Get Rid of Green Water in Fish Tank

You can get rid of green water in your fish tank by doing these 5 things: 1. Reduce the intensity of light to your fish tank, 2. Do a partial water change, 3. Stop Overfeeding, 4. Don’t Overstock your Aquarium, and 5. Clean Your Filter.

1. Reduce Intensity of Light to Fish Tank

You can get rid of green water in your fish tank by reducing the intensity of lighting. If green water is caused by strong aquarium lighting, try reducing it. You can also keep the lights off for a day or two and that will usually resolve the problem.

If the green water is caused by direct sunlight to your fishtank, then you should reduce sunlight by lowering the shade or devising other methods to block sunlight.

If you are getting too much sun to your fish tank because it’s next to a window, ideally you should move your tank away from the window. If moving your aquarium is not an option then try different ways to block sunlight to your fish tank.

In my case, when the water turned green in my fish tank, it was located on my desk, next to the window. The result of being next to the window is too much light and that caused the algae overgrowth and the water to turn green. I put up black out curtains to keep direct sunlight out.

2. Partial Water Change

You should do a partial water change to get rid of the green water in your fish tank. Use a gravel cleaner to clean the gravel off any algae remains and to siphon out water from the aquarium. Change 15% of the water.

3. Stop Overfeeding Your Fish

Overfeeding your fish means there is a lot of uneaten fish at the bottom of the tank. Every time you overfeed, organic waste accumulates in the aquarium. This will result in algae overgrowth which turns your aquarium water green.

Don’t feed your fish for a day. Clean your aquarium. And the next time you feed your fish, make sure you don’t overfeed. Only feed what they can eat in 1 minute. A small pinch of food will do. Remember, it’s better to underfeed than to overfeed your fish!

4. Don’t Overstock Your Aquarium

You may be overstocking your aquarium with too many fish. This will result in unusually high organic waste which triggers algae overgrowth. Overstocking your aquarium may be a reason why your fish water is green.

As a rule of thumb, stock 1 fish for every gallon of water. I usually recommend taking a conservative approach to this rule since you have aquarium decorations, rocks and plants- all this take up space. So a 10 gallon tank is actually 8.5 gallons once you deduct the aquarium decorations.

Use our How Many Fish in a 10 Gallon Tank Calculator and How Many Fish in a 20 Gallon Tank Calculator to help figure out how many fish to keep in your fish tank.

5. Clean Your Filter

When was the last time your cleaned your filter? It may be time to clean your filter. A dirty filter will result in too much organic waste which triggers algae overgrowth. Who knew your dirty filter is indirectly turning your water green!

When you clean your filter, don’t run the filter and filter cartridge under tap water! You will kill all the beneficial bacteria. Simply wash your filter and filter cartridge in a bucket of water from the aquarium. (Yes, the green water!)

How to Prevent Water From Turning Green Again in Your Aquarium

If you simply just changed the water in your aquarium and not do the other things I’ve suggested above, there is a high chance your aquarium water will turn green again! You can prevent future algae outbreaks in your fish tank. Here are things to do to prevent out of control algae growth in your fish tank.

1. Add a lot of Live Plants in Your Fishtank

Live plants can help prevent algae buildup in fish tanks. Add a lot of live plants in your fish tank. Plants will compete with algae for nutrients which will help prevent future algae outbreak. Live plants will ensure your fish tank water never turn green again!

2. Wipe Aquarium Glass Thoroughly

Every 2 weeks, wipe all four sides of your aquarium glass thoroughly with an algae scraper. This only takes 5 minutes of your time but is so worth it! Get an algae scraper that is extendable so you don’t have to stick your hand in the water.

3. Get an Algae Eater

Introduce algae eater(s) in your fishtank. Bristlenose catfish (Ancistrus temminckii) is an excellent algae eater and a good community fish. It does grow to 6 inches so you can’t keep it in small tanks. Another option is the Midget Sucker Catfish (Otocinclus affinis) these are small algae eaters and are good community fish. Get a group of 2-3 to help control algae growth. They are small and will grow to 1.5 inches.

If you want something different, get some Cherry Shrimp (Neocaridina davidi). Cherry shrimp are great algae eaters and will help control algae overgrowth. These algae eater(s) will help keep your aquarium water crystal clear!

4. Partial Water Change

Keeping up with partial water changes is essential in preventing aquarium water from turning green again. Every week, make sure to do a partial water change.

When you do partial water changes, don’t just take water out. Take the time to use a gravel cleaner to get rid of debris and organic waste buildup on the substrate. This will help maintain good water quality in your fish tank which is critical to keeping algae growth in check.

If you are like me and find gravel cleaning a chore, you might be using the wrong gravel cleaner! I used to hate doing water changes because I get frustrated pumping to get the water started in the siphon. Ever since I bought this gravel cleaner, changing water is a breeze! You don’t even have to stick your hand in the water to use the gravel cleaner! It’s that easy!

When you do partial water changes, always check the status of your aquarium filter. If the filter sponge looks dirty, simply take it out and rinse it in the bucket with old aquarium water. Remember, never rinse your filter under tap water! You will kill the beneficial bacteria.

5. Get the Lighting Intensity Just Right

Getting the correct light intensity to your aquarium is critical in preventing your water from turning green again. Pay attention to the amount of light your fish tank is getting, make sure you are getting just the right amount of light. Make adjustments if you have to. Get an LED aquarium light with timer that changes light intensity so you can be sure your fish is getting just the right amount of light.

Final Thoughts on Getting Rid of Green Aquarium Water

Having your aquarium water turn green is distressing, however, it is not difficult to fix. If you keep algae growth in check by making sure your fish tank is not getting too much light and if you keep organic waste level at a minimum with proper aquarium maintenance, then you should not have to experience your aquarium water turning green.