We know this. a 125 gallon tank or larger would be best for these fish. KNowledge that we already know. HOWEVER, I bet 90 percent of poeple that own tinfoils do keep them in 60 gallons or smaller tank. Is there something wrong with it? No. I am in fishkeeping for 1 year. HOWEVER, I grew up all my life with my dad tinfoils who never showed any stunted problems and looked perfectly healthy. I change water constantly and feed them properrly. Many fishkeepers change the water once a month or dont even care. I Do.
Cacti: Instead of getting that oscar, why dont you get that Distichidus Sex. or loulouso ? In the LFS (VERY few of them) I seen them for sale for 29.00. When they do get older, their colors do tend to not be so bright, But they still have the stripes. Or you might consider a Tiger shovelnose catfish. WOW they are one NICE catfish. I seen one in the LFS that was 2 feet long. NICE coloring. Now that fish I would not reccomend for a 60 or smaller tank. BUT cacti..for your 300 gallon tank...... Of course though, they tend to be boring I think. Just laying there and not swimming around and all small fish will be an immediate meal......