Ammonia Problem on a tank that's 1 1/4 years old

[domelotta]

I have had my 120 gallon tank up since the early summer of 2010. Originally I had one large piranha, but decided to add more over the months because he was not very active and of the Pygocentrus genus so he could have fellow Pygo tankmates. All in all by 3 months later there were 9 piranhas in there ranging from 6-10"+. Over the course of the next ten months they cut down their numbers and now I have 5 ranging from 8"-10"+. The problem I have, is that I have ammonia ranging from 1.5 ppm (today's test kit results) to 8 ppm on a bad day. The results are never steady and I have been trying every possible solution.

I have also cut down what used to be a jungle of a tank...a truly impressive site...to a semi-lightly planted tank because I thought the cause was dying roots (dwarf sag growing uncontrollably)

Everyone I talk to says to let it level out and do small water changes, but I have done that for the 5 months now. I still cannot get rid of the ammonia. I dose Prime with every water change, feed 2x-3x a week; a small bowl of raw shrimp soaked in vitachem and keep on top of siphoning excess waste particles.

My tank specs and equipment:
120 gallons
Fluval FX5
Rena XP4
AC110 HOB
Penguin Biowheel 200
Koralia 1200 GPH
AC Powerhead70
2 200 watt heaters
a couple pieces of Driftwood

Any help would be appreciated...Thank You

 

[dirtyboots]

overpopulation of the tank

 

[Bderick67]

What are your pH, nitrite and nitrate levels?

 

[KaiserSousay]

Was everything fine and then, Bammm, you are getting these readings?
Has ammonia been creeping up?
When did you service your filters last?
50% WC, every day wouldn`t be out of the question, given your ammonia results.
What do you mean by trying everything possible?
Overstocking means more attention to filter service and tank maintenance you know.