Oscars keep

Question
QUESTION: Hi Chris, my question is this.. recently i had bought this beautiful large oscar for my 75 gallon tank.. so far it was doing good.. then i did a water change a day or two ago.. everything was well.. i did another water change today because there was a high amount of poo under the sand.. later in the day my oscars went to the bottom and started to yawn constantly.. i got scared so i drove to the pet store and bought a powder that sets my ph to 7.0 . .  the oscars still keep yawning and sometimes come up for air.. are my fish going to die? or will it take some time for the ph to settle in for the fish.. i checked the ph after i put the chemical in and it was set to 7.0.. but they still keep yawning.. my ph now is a 7.0. i have two oscars.. and i have a cannister filter i replace it with 5 gallons of water.. the tank has been set up for about a year now

ANSWER: Hi Jeswin;

Oscars "yawn" when their gills are irritated. It's probably from an ammonia and/or nitrite spike after adding the second oscar. Make a 25% water change right away and check the levels of ammonia and nitrite in the tank. You can get test kits from your fish store to monitor them. Do a 25% water change every day that the ammonia or nitrite are elevated. Ammonia will begin to drop in the next few days and then nitrite will start to rise. The ammonia should go away but nitrite may stick around for a few more days. Test for both every day until they both go down and stay down.

Normally the ammonia is handled by the beneficial bacteria that lives in your filter, gravel and decorations. But, the fish population or "bio-load" in your tank is now increased. The beneficial bacteria in your filter needs more time to grow larger colonies to handle the extra ammonia (waste) from the new fish.

I hope they do okay...

At Your Service;
Chris Robbins

---------- FOLLOW-UP ----------

QUESTION: thank you so much.. my oscars are doing excellent now.. another question i have is this.. i have crushed coral as a substrate.. the fish store tells me that this is the problem why my ph is going high all the time.. if i was to change to sand would it be a smart idea? and if it is what type of sand is good so i can avoid it being sucked up the filter

Answer
Hi Jeswin;

I'm so glad they are better! The coral sand is indeed what is causing the elevation in pH. It is meant to be used in saltwater tanks only. Just use any small aquarium gravel available in fish stores. Sand is so small that it can plug up filters as oscars move it around.

At Your Service;
Chris Robbins