Why do my Oscars keep dying?

  • We are currently upgrading MFK. thanks! -neo
Unless your sand came from a toxic Super Fund site, it is not the problem. As stated by others, its your lack of frequent water changes. Oscars are very sensitive to poor water quality, for most people that don't do enough water changes, (although they don't always die), the oscars get disfigured by hole in the head disease. Because a 55 gal is a small tank, you need to really especially vigilant with water changes.
 
Without beating a dead horse, I’ll try to give my suggestion. Two Emperor 400’s is enough filtration and the bio-wheels are a nice feature. IMO it’s the cartridges where they fail IMO. I don’t like using carbon unless I’m removing meds and people don’t change them enough. I have one on a 75 gallon tank and use it for bio-filtration only. I fill the area where the cartridges are supposed to be with bio-media, ceramic rings etc. you could use one of yours this way and use the other for mechanical filtration.

Oscars are great fish but they are very unforgiving of water quality issues. The best way to handle this situation IMO is to test the water for ammonia, nitrite & nitrate. Obviously any presents of ammonia or nitrite would indicate and un-cycled or cycling condition. However high nitrates (in this case) over 30ppm indicates not enough maintenance in the form of filter cleaning, substrate vacuuming (removing of uneaten food or other organic debris from the substrate) and adequate water changes.

The best way to judge is by testing the water, ideally you want your nitrates below 10ppm for Oscars. A 55 gallon tank is a double edged sward the down side is you will need to do more water changes the up side is in a small tank like that you could do twice weekly 50% water changes in no time. Also do not over feed which is very easy to do especially with Oscars because they always act like they are starving and they grow like weeds. In addition if you get rid of the Plecos you’ll notice your Substrate will be cleaner without the spaghetti like Pleco poop all over the bottom. I would also keep only one Oscar. Get the water issue under control and only add another once you get a tank at least 125 gallons, your fish keeping will be more enjoyable and less of a job.
 
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