Oh boy. You really should have researched this more.
1. Oscars need a 75 or more. I'd get rid of it now, while it's still small and might not be stunted yet.
2. Goldfish and tropicals do not mix. They need cool temperatures, 68-72, and tropical fish need higher, around 72-78. If they're not fancy goldfish, that is, if they're common ones, they don't belong in something like a 55 either. They need ponds.
3. What kind of sucker fish are these? If they're plecostomuses, they need to go as well. They will get huge.
4. Lights won't affect your fish.
5. PH is fine.
Did you cycle the tank? Here's some articles on fishless cycling:
http://badmanstropicalfish.com/articles/article14.html
http://www.wisegeek.com/what-is-fishless-cycling.htm
Good luck, let us know what's happening.
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current setup:
15 gallon, planted w/ pressurized co2, 55watts PC lighting, EI fert dosing.
-5 harlequin rasboras
-7 Aspidoras pauciradiatus (sixray or false corydoras)
for reference: my name is Julie
