Water in my tank keeps turning green, any suggestions?!?

Question

I currently have a large 55 Gallon Tank with two Tetra 30-60 Power Filters. I have large fish (Oscar & Pacu) and a Red Tail Shark and 2 Plecos. I change my filters every 2 weeks (that would be a total of 4 filter cartridges since each filter holds two catridges). I also have to do a 50% water change EVERY WEEK since I have large fish in my tank. They are fed twice a day (once when I wake up and then again at night when I get home from work) but they aren't given a large amount of food. I use my water conditioner as directed, I also add salt to my water as well. And yet, my water will stay clear for a few days after the water change, but then it rapidly turns green within the week, and it's hard to see my fish in the tank! I heard that I need to leave the light off for a few days. Will this work? I only have the tank lights on during the day while I'm at work, and then I turn them off before bed. Even with that said, the lights are on more than they are off.

My filter system has two types of cartridges one is a BIO filter that I'm not supposed to replace and then the carbon filters that I replace every two weeks. Does this make any difference??

Answer 1

Well, your tank is WAY overstocked. Oscars need a minimum of 60 gallons of water each. Pacus can reach 3 feet and need THOUSANDS of gallons of water.
Plecos are 2 foot fish and should not be kept in anything smaller than 100 gallons. Your red-tail shark will likely be eaten by the Oscar eventually, as oscars grow up to be voracious, aggressive fish.
Please consider properly stocking your tank. You should return to the petstore or sell your oscar, pacu and plecos - or get a bigger tank for them - and stock your tank around the red-tail shark.

It is this overcrowding that is causing your green water. Green water, which is a single-celled algae, needs two things to grow: light, and nutrients.

Reduce your photoperiod - invest in a 5$ timer and set your lights to be on for 10 hours per day.

However, on my tanks I do the same as you (turn on the tanks in the morning and turn them off before bed) and do not have an algae problem. The main issue with your tank is the overcrowding.

Your fish are producing huge amounts of ammonia, which is feeding the bacterial colonies.

If you want a healthy tank, you MUST either get a bigger one, or get rid of more of your fish, because those fish can NOT survive and be healthy in a tank that small.

In the meantime, do 40% water changes, twice a week, to keep ammonia levels down. When you have a properly stocked tank, you can do 20-30% once a week.

A blackout, as described by judy_r8 (keep your tank in total darkness) will kill the algae for a while, but you need to fix the root of the problem ,or the algae will just come back in a couple weeks.

Answer 2

You should cut your light cycle back. the water may be turning green because the algae is able to grow with so much light. My recommendation would be to only run the lights when you are at home before you go to sleep...say from 5:00 - 9:00 p.m. This will hinder algae growth but not bacterial growth (which you need to process ammonia and wastes in your tank.) I don't know how many fish you have in your tank or how big they are, but if you have several large fish, your tank may not be large enough. I'd say that a 55 gallon is too small for any more than 2 pacus or oscars, especially if they are large. If you can get a larger tank, I would highly recommend that. Good luck!

Answer 3

Hm... well, goldfish tend to be very messy fish and will dirty up your tank in an instant. That could be why your tank is getting cloudy first. Regarding the green water it does sound like algae, even though it is not on the side of the tank. Acrylic tanks grow algae more because they scratch easier (making a nice home for the algae to grow). I got a glass tank and don't have near as much trouble. You could try an algae killing liquid but make sure you have no invertebraes, I believe it can hurt them. The most important thing is... keep your tank out of direct sunlight! That will cause excessive algae growth. Hope this helps!

Answer 4

You are fooling with the balance of algae in the tank by changing the water too much. I had the same problem with one of my tanks, I tried everthing I could think of, then someone told me to cover the tank so no light got in except when I was feeding the fish. It took about 10 days to clear up, but the tank is now the clearest of all three I have. Stop the water changing totally for this time, (your fish will be fine! algae actually produces oxygen)and feed them a little less. I also just rinsed the filter off instead of changing it for the 2 weeks before and after..

Answer 5

Too many fish in the tank. Don't change your media in your filters. Instead put the open celled foam for Hagen's aquaclear filters in your filters ( instead of the cartridges it comes with ), and rinse them in dirty tank water every few weeks.

Get rid of all of those fish except the oscar and shark.

The water changes you are doing are fine and your lighting is fine.

Green water is caused by too much poop and not enough mature bacteria colonies in the filters. The filters that have replaceable cartridges always do this to peoples tanks.

Answer 6

Hi there,

Stop doing 50% water changes its way to much, try only a third from now on, also go out and buy some bristlenose catfish(suckerfish) they will improve your tank straight away, by cleaning everything.
With the light cut it down to around 10 hrs a day and leave the filters alone for around 2 weeks, as u need to build up some sort of bacteria in your tank for the well being of your fish.

good luck with it all

cheers

G

Answer 7

You need to put an algae fish or two in your tank. Also, make sure the tank is not sitting in an area where there is alot of sun light hitting it. You can buy algae tablets also but I have always had a couple of algae fish and that is their job is to eat the algae.

Answer 8

It's from too much light. Either direct sunlight or the wrong kind of light. Fluourescent lights are much better - the fish' colors look much more natural, too.

Answer 9

Could be something wrong with the filter or the light.

Answer 10

my best friends dad said so take the tank away from the window or where ever else it is getting the sun from and something else that could help is to go and get a artifical moonlight lamp.