hello, i have a problem. i have a few piranhas in a 150 gallon tank, they're still only about 3 inches a piece, and i cannot seem to get clean water. theres a cloudy green tinge to the water so bad sometimes i cant see the back of the tank. i mentioned it to a couple guys i work with and they said it was because of the diet i keep them on.i figured id ask again here and in the piranha forum because mechanics giving fish advise seemed a little out of place. they eat store bought fish, cut up and frozen, i don't remember what kind exactly, but i'm running low so will have to go out and get some more in a couple days, iirc it was the cheapest stuff they had. anyway, i haven't tested my water in a few days but at last test everything was fine and im running a fluval fx5. water changes help, but by the next day it looks like i haven't done anything. theres some rocks, new pool filter sand, plants, and a plastic tree looking thing from petsmart. the plastic decoration does have some algae on it from a previous set up and its hollow as well. Im thinking thats just full of algae and leeching it into the water maybe? theres no real wood, tea leaves, black water anything in the tank and i thought the fx5 would take care of my problem. any ideas?