tank turning green

Question
Good evening. At work we have a 5 gallon tank (I think that's the size) with one goldfish in it. We feed him 2x and day, but it seems that within 2 weeks his water always turns green. These days the plastic plants and rocks at the bottom are turning brown/green as well. He has a filter and we turn the light off during the day. It's only one darn fish (he is fat) why is this happening. Also, what is the correct amount/times to feed the goldfish. Thanks so much!

Answer
Hi Tamara;

He's just getting too much food and not enough cleaning. His tank is also too small for him. Goldfish really need at least 10 gallons per fish and powerful filtration to thrive. His wastes are creating a perfect environment for the algae that is thriving in there. Fish waste is 'fertilizer' for it. Feed only enough food for him to completely finish from all areas of the tank in 2 to 3 minutes. If you were feeding once a day, he can have enough to finish in less than 5 minutes. The idea is to let fish feed for no more than 5 minutes every day whether fed once, twice or more times a day. Change 25% of his water and vacuum the gravel every week. All tanks should be cleaned weekly for the best fish and tank health.

Here is a great web page about goldfish and their needs to help you know more;

http://www.firsttankguide.net/goldfish.php

At Your Service;
Chris Robbins