high ammonia with oscars

Question
I have 2 Oscars in a 75 gal tank with a cascade canister under cabinet filter. (not sure if 700 or 1000)media fits both.   It was set up 7 mo ago(July) they are 4 yrs old given to me by my nephew who never had ammonia problems. The ammonia has been rising slowly for the past 2 mo it is now at 6.0 the ph is 6.2.  I added 2 large pieces of driftwood in aug.   I do 20% water changes every 2-3 weeks.  I recently did a 40 water change Dec 18, cleaned the entire filter and hoses, changed ammo chips and rinsed carbon, advised by a pet store person.  The last filter media changes were Oct 20. The bio filter has not been changed only rinsed  since i have had the tank and before.(9-10mo)
The ammonia is still high and ph low. They are eating. Today I did a 20% water change/vac.  I noticed today one is starting with hole in head. I read coral rocks can help raise the ph that will help ammonia drop? What else can I do to drop the ammonia if anything thank you for any help

Answer
Hi Fran;

Oscars are pretty messy guys so they need a 25% water change and gravel vacuuming every week. Taking out the driftwood will really help too. Driftwood acidifies the water and lowers the pH. It will take a while, but the pH should begin to rise and the ammonia should stabilize as the tank balances again. Don't add coral rocks yet. Just removing the driftwood and performing more frequent water changes will probably be just fine. The ammonia problem is associated with excess waste in the system but may also be from the acidic water killing off the beneficial bacteria. The bacteria consumes ammonia usually, but if the pH is too low, beneficial bacteria begins to die and ammonia rises.

Something simple that helps along with water changes and avoiding wood is adding bubbles to the water. A long airstone on a good sized air pump in your big tank will look nice as well as helping to keep the water oxygenated better. The beneficial bacteria will really thrive from that. I have seen tanks improve in just a few days after a chronic water problem from the simple addition of bubbles. When the bacteria colonies are suffocating, they can't do their job.

Hole in the head is a symptom of chronic high nitrates (NO3) and sometimes malnutrition. Those weekly water changes and feeding a good nutritious diet will help a great deal. Here is an excellent web page about it;

http://www.flippersandfins.net/HITHarticle2.htm

I hope all goes well.....

At Your Service;
Chris Robbins