CichlidFish.com - Fish That Think.

Hi everyone, ive got a question for you..... Im having trouble keeping the nitrates down in my tank, they arent high, but i dont want them to get to point that they are dangerous.  My tank is 55 gallon with three 2" inch ocars (planning to go to a 200 when they get a little bigger). Ph is 6.6, water temp is 77 degrees, KH is at 0, GH is 120, nitrite and ammonia are at 0, but nitrate is over 40 ppm and wont budge. I do a 25% water change weekly, vaccuum the gravel, and have even tried nitra zorb and nothing seems to work. I tested my tap water and there are no nitrates in it, so that isnt the problem either..... anyone have an idea??   

Three 2" fish in a 55 shouldn't be causing a lot of problems.  Anything else in there with them?  What kind of filter are you using, and how often do you clean it,?

Beyond those 2 questions, and knowing young Oscars, I'd bet that they're conning you into feeding them too much.  As I'm sure you've noticed, they're very sloppy eaters, and the leftover food tends to decay.  They don't need nearly as much food as they would have you beliieve!.  Try going to a 50% or more water change instead of the 25%. 

Good luck!

No, the oscars are by themselves, i wanted to make sure i didnt overstock. The filter is an external aqua clear 50.... maybe i should add another one to the tank, do you think that would help?

I will def try changing more water though, i just wasnt sure if it was ok to change that much at one time.

Long-term, you'll probably need a bit more filtration than that for keeping Oscars.  For now it's probably fine.  The thing with nitrates is that in a freshwater tank you only have 3 ways of dealing with them:

1.  Prevention (keeping the bioload down, not overfeeding, etc)
2.  Plants -- plants will use the various nitrogen compounds for their growth.  However, keeping plants with large cichlds is very tough.
3.  Dilution (water changes).  Without going into the math (makes my brain uncomfortable), unless you're replacing over 50% of the water, the percentage of nitrates (and other fish-generated chemicals) will continue to slowly build up.  David Boruchowitz, of TFH magazine, has written extensively about this.  He did a long-term experiment of daily 90% water changes with a tank of Oscars.  Part of the idea is to simulate the natural replacement of water in a stream -- only the stream is from your pipes.  I personally don't have time for that kind of regimen.  I change about 50-70% twice weekly.  Plenty of people do fine with less drastic changes, and many species likely wouldn't tolerate it.  However, if you're having nitrate problems, changing larger quantities of water would definitely help.  Also cut down the feeding, of course. 

I do a 20 -25% change weekly but also keep a nitrate reduction resin in one of the filters at all times.  This keeps my nitrates down around 10ppm