Growing out potentially large fish in a 30 is one thing, forcing them to survive in a 30 for life is another. Stunting a fish to force it to live in inadequate housing happens all the time, both intentionally and unintentionally by many people. If you continually provide a fish with the bare minimum of their diet or reduce a major part of their nutritional needs and then compound that by keeping it in a small tank, yes, the fish will be stunted and survive in the situation provided. That isn't proper growth or responsible fish keeping IMHO. We try to help each other make responsible decisions that will benefit both our hobby and our fish. Suggesting that stunting an Oscar and keeping it in a 30 gallon tank for ten years is really not contributing to the responsible information that many come to this site to share and receive. You can get that sort of misinformation on random Google searches. But as you say, it can be done. I just believe that it shouldn't if one is trying to provide the minimal best for any large cichlid. I also know that at times people can go to extremes when it comes to suggesting minimal tank sizes for particular fish. Personally, I'd rather have a fish with way too much room than one with barely enough to move. Feed a fish NLS, Hikari, Xtreme, veggies...whatever you want, just have a realistic approach to keeping large fish. If you can't buy the proper tank, don't buy the fish. I'll leave the in depth nutritional studies of Cichlids to those members who are more versed on the subject than I am. I hope all of this helps the OP to make a good decision.
