sick tank

Question
I have kept a 65 gallon tank for 4 years with two oscars in it.  I "inherited" the tank after it was abandoned by my boyfriends roommate.  The oscars were sick when I recieved them (hole in the head and open sores).  They were well for awhile but the HOTH never went away completely.  At any rate they have both recently (one two weeks ago, one last night)died from a bacterial infection.  I miss keeping them and want to adopt two adult oscars (from an owner who didn't know the would get big LOL) However, I am afraid to put them in my tank.  Is there some elaborate decontamination process I have to go through?  Do I need to cycle it again?  If so will it cycle with two adult oscars in it?  If not what fish could I cycle it with that the adult oscars won't just eat?  How can I even tell if my filters are still alive?

Answer
Hi Liz;

Poor guys. I wouldn't worry about the bacterial infection being in the tank itself. It was on the fish from being weak. If they were subjected to bad water quality while they were growing up before you got them, this undoubtedly affected them in their adult life. Fish like them need especially clean water for the rest of their lives to stay healthy.

If it was my tank I would drain all the water out while vacuuming out the gravel to get most of the crud out. If there is still a lot of crud in the gravel when you get to the bottom, refill the tank again and vacuum the gravel while draining a second time. This should preserve a lot of the beneficial bacteria in the gravel but still remove the excess waste and old medication (if you used any) that has built up in there. When you put the new fish into it, they will cycle it just fine if you make frequent water changes to counteract the toxins that may build up. It will go through a "Mini Break-in" and won't be too bad as long as you don't feed them much. Replacing 25% of the water every three days may be necessary for awhile, so monitor the ammonia and nitrite levels for the first couple of weeks as it settles in.

As for the filter, just gently rinse the media and re-use it. If it plugs up again after the fish go in, rinse it again. Very rarely should filter media be thrown out. It is an important place for beneficial bacteria to grow. For example, I have a 55 gallon that is filtered by a Fluval 304 canister filter. I rinse the media every 4 to 6 months and I think the last time I used any new stuff was over a year ago. My tank is crystal clear all the time and the fish thriving and healthy. It is maintained by gravel vacuuming and a partial water change of 25%.

Oscars are such big messy guys that you really need to make partial water changes often to keep them in good health. Once the "new tank" crisis is over change 25% of the water once a week while vacuuming the gravel. It is important not to overfeed them as well. Feed a good quality pelleted food to avoid excess wastes. Feeder goldfish, worms, crickets or cheap pellets have way too much excess bulk in them that the fish can't digest. They just make a mess in the tank. A good quality pellet will also give them all the vitamins they need. OSI, Hikari, and Tetra have very good cichlid pellets. They seem expensive, but being a more concentrated food you get more real food for your buck.

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Chris Robbins

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