Constantly Dirty Aquarium

Question
We have a 5 gallon plexi tank with a Bio-Wheel filtration system. It's been set up for about 1 & 1/2 years now. We have 2 penguin tetras and 2 serpae tetras in it. And the test strips we use test normal on all criteria.

My question is, why is our tank ALWAYS dirty? We have to do full water changes about once every week and half to two weeks. And that's pushing it, because the water starts turning green after only a couple of days. That's the odd part, all of the 'stuff' in the tank (the rocks, the plastic plants, the little cave) is relatively clean, it's just the water.

The water gets almost totally green within about a week or two, even though there's no obvious algae build up on anything else. And the fish seem just fine and happy.

We're starting to think maybe our tank is just too little...could that be why the water gets green and murky so fast? The Bio-Wheel filter says it's good for tanks up to 20 gallons...maybe we just need a larger tank.

Thank you in advance for your help,
Abi

Answer
Hi Abi;

Your tank has what is known as "planktonic alage". It is a type that is just suspended in the water. There are many possible causes but most experts seem to agree that it is simply water chemistry. Some water sources just have enough of what it needs so it goes crazy. What that specific need might be is what we can't agree on. Some say phosphates, some say nitrates, others say too much light. Since these are all naturally occuring elements, we just don't know for sure. It could be the size of the tank too and it just concentrates the waste enough for just long enough to cause it to stay green. Whatever is going on, the algae likes it.

Start first by limiting the light that gets to the tank and cut back on food. Make sure the tank gets no sunlight and the hood lights are on only 8 hours a day. Feed once a day, and only enough for the fish to eat all of it from everywhere in 5 minutes or less.

Extra aeration and adding live plants is helpful too. The plants compete for the same nutrients and will also shade algae out. The aeration keeps the water oxygenated and suspended algae doesn't seem to like that much.

Here are some web links that may help too;

http://www.nunnie.com/cloudy.html
http://www.ponddoc.com/WhatsUpDoc/WaterQuality/GreenWater.html
http://www.totallyfish.com/tips/greenwater.html

At Your Service;
Chris Robbins