Ok, from reading the posts, I know that we have too many Oscars in our tank and that's why the middle size one is beating the heck out of the larger fish and occasionally attacking the smaller one. We plan on removing the aggressive one ASAP. However, the larger one hardly has any scales left on the one side of his/her body. Would you advise on how to help this fish get back to healhy state. Thanks!

Plenty of water changes and try myxazin( remove carbon from filters 1st).

You can put a divider in the tank (to separate any aggression) ,just get a piece of glass cut to the right size and use a few suckers to hold it in place. However this is only a temporary solution till you get rid of the aggressor

Hi and welcome!
(I love those posts that start off with a simple HELP!)

How big is the tank (gallons)
How many Oscars and their sizes?
How many other fish and their sizes?
How often do you do partial water changes?
Do you know readings for ammonia, nitrites and nitrates?

Do you have a quarantine / hospital tank available?? size?

have any meds available to you?

have any photos of the fish? especially the injured one?

Lots of questions, but will help with answers...

How big is the tank (gallons)-- "55"

How many Oscars and their sizes? -- "3 Oscars 6 to 7 inches"

How many other fish and their sizes? -- "1 algae eater 4 to 5 inches"

How often do you do partial water changes? -- "once a week - just started increasing did it last night"

Do you know readings for ammonia, nitrites and nitrates? -- "no? don't even know how to do this"

Do you have a quarantine / hospital tank available?? size? "No, but we have a tank downstairs with a blue lobster in it. would the oscar attack the lobster?"

have any meds available to you? "No but we can get what is needed -- do you have suggestions on where to get the meds quickly. We live in chicago, il USA "

have any photos of the fish? especially the injured one? - Yes, see the attached. Hopefully it's there.

Thanks for your help

trying to send the photo again... we take pics at high res.

the 55 is wat to small of a tank for your oscars, 1 max is all for it. common plecs are not a good idea as they create more waste than they clean up. keep with the water changes maybe 2 or more per week. go out and get an aquarium pharm. master test kit at your lfs asap.read the instuctions carefully and start your testing. how big is the quarentine tank? the oscar may or may not leave the lobster alone, doesnt sound like he is in any condition to mess with much. dont want to steer you wrong on the meds as I ve never had to use any but someone will be able to let you know for sure. work on getting a pic posted. take care,
mike c.

The tank is too small for two Oscars, never mind three. You already know that though so you need to get your fish load way down and the 55 will hold the two Oscars remaining for a short time because they aren't fully grown.

Remove the aggressor but understand that Oscars in general fight with each other, especially two males. But its hard to sex them so that is not a quick answer. Depending upon how big that lobster tank is, you might use that for a hospital tank if the lobster is big enough not to be eaten by the Oscar that needs healing, and the tank has to be big enough for him anyway, say at least a 29 and hopefully bigger. Otherwise, you need to treat the entire 55 to help that bigger wounded fish.

Partial water changes of 30-35% on an increased schedule are going to be required to help the fish heal too. if you currently do that weekly, plan on at least twice a week or more until he is completely healed.

You really do need to get yourself a master freshwater test kit and begin to understand what is going on inside yout tanks. Crystal clear water that may look great to you may in fact be fouled with ammonia or nitrites, both of which could end up being deadly to your fish.

I really would love to see a photo of the injured fish before steering you to to a medication (or several) as it will depend upon severity. Often oscars do injure or cut themselves and frequent water changes is enough to heal them up but in your case you will most likely need some meds in the tank.

What kind of filter are you running and do you use carbon? You shouldn't use carbon at all with oscars and especially while uing any meds. Post that pic if you can please and find another tank or home for that one aggressive fish temporarily. Your tank is too small to use a divider and you wouldn't want solid glass anyway as you need to keep flow throughout the tank..