How To Combat Green Water In My Aquarium?

Q. I have Koi aquarium and the tank is placed outdoors. The water also started turning greener and greener. I replaced part of the water once, but it still turns dark green very fast, and I am unable to see my fish clearly (and it seems that three of my small sucker fish have disappeared.) Though my friends have assured me that this isn’t a problem, I would like to know what caused the water to turn greenish? Please advise me if I should continue to replace the water.

Why Aquarium Water Always Turns Green?

There are few reasons why the water always turns green, even though you may have changed the water:

1. Because your tank has not matured, the bacteria in it cannot compete fast enough for the same nutrients as the algae. Hence the algae have the upper hand and are always growing at a much faster rate than your bacteria can strip off their food source.
2. As your fish grow, you tend to feed them more. Thus, byproducts are produced at a faster rate than can be converted by the bacteria, and these create excess food sources for the algae to thrive on.
3. Your tank is exposed to plenty of light, and this encourages algae growth.

How To Combat Green Water In Aquarium?

To combat green water, you need to understand the nitrification cycle, and “help” the bacteria by:

1. Stocking fewer fish initially.
2. Feeding less—it won’t kill your fish if you feed them every other day!
3. Checking the aquarium parameter at least once a week. Maintain the water quality through routine water changes. Replace at least 30 per cent each week.
4. Shielding off strong light if possible.
5. Dosing with bacteria weekly, and then fortnightly.
6. Always adding a chlorine remover or water conditioner to “new” water. This helps to reduce the amount of chlorine (which no living thing takes well to) in the water—which can sometimes kill the more sensitive species, and kill off your colony of good bacteria within seconds.

Beside the above consideration, it is also important to look into the size of your filter and determine how long it takes to reduce the greenness of the water. An undersized filter would take forever! If you are rearing koi, an ideal ratio of filter size to total water volume is 1:3. An undersized filter means less tolerance for deviation, and this will swing the equilibrium out of sync frequently, making it more difficult to rectify the green water problem.

If you still encounter this problem after managing to do all of the above, it looks like stocking fewer fish would have to be the best solution.

Green water is actually good for the fish as it supplies them with a ready source of food, and shelters them from exposure to strong sunlight. But on the other hand, what’s the point of keeping koi if you cannot see them!

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