EDIT: they aren't all 4 inches ??oscars are 4 inches each and NTT is about 7-9 inches it's hard to tell when he is in the water. Also forgot to mention I have a severum in there who is about 4 inches also. Haven't had him for long and I forgot to list him as being in the tank
Ahhhh....
Okay, I added the extra fish (severum) and upgraded the size of the dat. You have ~.45 lbs of fish, and per your other post, you only feed prawns (which are 83% protein.) WC is 5 gallons per day with a 30 gallon change weekly.
I can get to 80 ppm nitrates on my spreadsheet, using a feeding regimen of 12-14% net body weight fed per day. That implies 55-60 grams of prawns per day, which is ~8 prawns (61-70 count.)
1) 12-14% feed per day seems like a lot to feed fish (to me anyway)
2) 83% protein foods 100% of the time seems too much
3) changing 3% per day and another 20% at the end of the week, seems too little
To look at it a different way, since total protein being put into the tank is what drives nitrates, the amount going in this tank is about the same amount one would feed four 13" inch Oscars on a daily basis. If you can't keep up with the WC (which is understandable), then I'd try either using lower protein foods or reducing the amount of prawns, preferably both.
i do fin level water changes every week on my 180, matter of fact all my tanks, better to much than not enough and you there doing it any ways why not change as much as you can?
