I have a 55 gallon aquarium inhabited by 1 7-8 inch Oscar, 2 Jack Dempseys (1@5-6 inches, 1@4-5 inches), and 1 12 inch or so plecostomus (nevermind the spelling).
I use a powerhead to circulate water, and a filter thingie that hangs over the back (assured by the pet store at time of purchase this was the proper size for the aquarium).
I have 2 inches of large gravel on the bottom of the aquarium- at least I did before the oscar decided to rearrange it mostly into the corners, and bare in the middle. I have a pseudo branch thing in the aquarium also. The setup has not changed in 7 months.
I feed the fish 2 dozen or so goldfish or 3 dozen minnows 1-2 times per month, with pellets a few times a week, and the occassional algae wafer for the bottom feeder.
THE PROBLEM: Green water. The color ranges from light green sometimes to “can’t see the fish unless they are right against the glass” dark green. It kind of cycles from bad to worse and back.
Sometimes, after a feeding, the water smells, so I do a 1/3 or so water change with water that has sat out for 24 hours. I also change the filter cartridges at that time.
Now that the sun is out more often, I am getting a bit of algae on one small side (the aquarium is in a corner, out of the sun, but if I open the blinds, it gets a little direct sun on one small side for a few hours in the afternoon).
Any idea what the green is, and how to get rid of it?