IF he is rubbing on objects, then that means a couple of things:
1. the pH has droped to low from where it was at normaly.. LIKE it was 7.4 then it went to 6.8 in less than 24 hours.. This irratates them so they rub on objects.. Check the pH when U see them acting off, doing routine VACS of the gravel and keeping YOUR filter clean helps prevent this.. With a Oscar, a good 30% of your tanks gallons is reccommended.. To figure this out,
say your tank is a 55 gal.. 55x .30 = 16.5 gal of water OUT/IN. As this is close to 15 gal then do that so U can measure the dechlor/salt/other better..
2. High Ammonia to HIGH NITRITES.. Either one can do the same.. these two should always be 0ppm in your tank IF cycled.. IF the pH crashed then Ammonia is the blame most times. .the best way to delute theses down is to do a WATER CHANGE and clean the tank /filter if it has not been done in 5 days..
3. ICH. this is a parasite that is like someone sprinkled salt on them.. These mostly FIRST show up in the fins.. they Rub as they do suck fluids on the fish so they itch.. LOW temperatures then HIGH temps cause ICH,, And stress from other picking on them to being new to the tank.. ICH does not like salt OR high temps.. ONE tablespoon per 5 gal should be used in the tank regardless if U have ICH or not.. ONLY get Aquarium SALT to do this with.. Do not TREAT for ICH if U are unsure if they have it.!!..
4. Temperature too HIGH. best to keep it at 76F OR 78F ( 24c - 24c) to warm and they get kind of aggressive, to 80F ( 26c +) and up,, They swim around trying to find a mate and get MORE aggressive, Best to keep it lower in temp...
I have found in all my tanks especially with BIG cichlids, that only 2" of gravel is fine.. Any more and it collects to much waste and uneaten food.. IF U have more than 2", on your next water change, I would remove it to this amount.. A UNUSED NEW small plastic dust pan works great to remove gravel with.. This wil also make it easier to VAC on tank/filter cleaning day..
YES U need a better filter. Get a Emperor with bio-wheels.. this wil help keep the tank seeded with good bacteria and help more with water quailty in the tank with big cichlids. Depending on how big the tank is, IF OVER a 29 gal, ONE Emperor 280 OR a Emperor 400, wil do U good.. IF bigger, say 55 gal and UP, then TWO Emperor 400, one per side wil keep your tank VERY clear..
IT is cheaper to get them on LINE.. U can get TWO filters for the price of ONE at any LFS..
Petsolutions has them on sale: http://www.petsolutions.com/Emperor-400 ... 2+C19.aspx
the 280 can be found on the right side..