Hey, could an Oscar live in a 40g breeder with an aquaclear 70 and I would vacuum the gravel every sat. and every wed. do a water change?

An adult Oscar, no. The minimum permanent tank size for an adult should be a 55g. A 40g is fine if its a juvie or if you have plans to upgrade in the future so long as you clean it thoroughly.

But the problem with this isn't just keeping the tank clean, but not having enough swimming room. An adult crammed into a 40 breeder its whole life will get stressed out. They're powerful and fairly active fish.

I don't agree with any of the answers you received A 40 breeder is a great tank .It provides more living space than 55 A 40 breeder is 36" X 18" for a total of 648 sq in of surface space .A 55 gal is 48 X 12 " for 576 sq in of surface space .The rest of a 55 is in the height. Tanks with more surface area can house more fish than those with more height due to more air exchange and usable living space. You have a good plan with your water changes

My black moor has white spots/ fungi all over and its tail is disintegrating, I have removed it from my 30 gallon tank and isolated it so it doesn't affect my 2 goldfish. I have bought and tried anti white spot treatment but seems to be getting worse since I used it. This is the 3rd black moor I have had in 3 month, I have a sufficient pump/filter and do a 10% water change every week. I have taken a water sample to pets at home who have tested it and said it is fine. I cant bear to lose another fish, I feel so cruel but surely it cant be so hard to keep them alive. What am I doing wrong?

No, no, and no. No Oscar will remain healthy if confined in such a small space even if you keep the water quality great.

Note: Oscars in tanks smaller than about 100 gallon always develop illnesses and never look good at about two years old

yea